diff options
| -rw-r--r-- | include/linux/frontswap.h | 7 | ||||
| -rw-r--r-- | include/linux/shmem_fs.h | 3 | ||||
| -rw-r--r-- | mm/shmem.c | 267 | ||||
| -rw-r--r-- | mm/swapfile.c | 433 |
4 files changed, 319 insertions, 391 deletions
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h index 011965c08b93..6d775984905b 100644 --- a/include/linux/frontswap.h +++ b/include/linux/frontswap.h @@ -7,6 +7,13 @@ #include <linux/bitops.h> #include <linux/jump_label.h> +/* + * Return code to denote that requested number of + * frontswap pages are unused(moved to page cache). + * Used in in shmem_unuse and try_to_unuse. + */ +#define FRONTSWAP_PAGES_UNUSED 2 + struct frontswap_ops { void (*init)(unsigned); /* this swap type was just swapon'ed */ int (*store)(unsigned, pgoff_t, struct page *); /* store a page */ diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h index f155dc607112..f3fb1edb3526 100644 --- a/include/linux/shmem_fs.h +++ b/include/linux/shmem_fs.h @@ -72,7 +72,8 @@ extern void shmem_unlock_mapping(struct address_space *mapping); extern struct page *shmem_read_mapping_page_gfp(struct address_space *mapping, pgoff_t index, gfp_t gfp_mask); extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end); -extern int shmem_unuse(swp_entry_t entry, struct page *page); +extern int shmem_unuse(unsigned int type, bool frontswap, + unsigned long *fs_pages_to_unuse); extern unsigned long shmem_swap_usage(struct vm_area_struct *vma); extern unsigned long shmem_partial_swap_usage(struct address_space *mapping, diff --git a/mm/shmem.c b/mm/shmem.c index b4d27ef87496..283a1833dafc 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -36,6 +36,7 @@ #include <linux/uio.h> #include <linux/khugepaged.h> #include <linux/hugetlb.h> +#include <linux/frontswap.h> #include <asm/tlbflush.h> /* for arch/microblaze update_mmu_cache() */ @@ -1093,159 +1094,184 @@ static void shmem_evict_inode(struct inode *inode) clear_inode(inode); } -static unsigned long find_swap_entry(struct xarray *xa, void *item) +extern struct swap_info_struct *swap_info[]; + +static int shmem_find_swap_entries(struct address_space *mapping, + pgoff_t start, unsigned int nr_entries, + struct page **entries, pgoff_t *indices, + bool frontswap) { - XA_STATE(xas, xa, 0); - unsigned int checked = 0; - void *entry; + XA_STATE(xas, &mapping->i_pages, start); + struct page *page; + unsigned int ret = 0; + + if (!nr_entries) + return 0; rcu_read_lock(); - xas_for_each(&xas, entry, ULONG_MAX) { - if (xas_retry(&xas, entry)) + xas_for_each(&xas, page, ULONG_MAX) { + if (xas_retry(&xas, page)) continue; - if (entry == item) - break; - checked++; - if ((checked % XA_CHECK_SCHED) != 0) + + if (!xa_is_value(page)) continue; - xas_pause(&xas); - cond_resched_rcu(); + + if (frontswap) { + swp_entry_t entry = radix_to_swp_entry(page); + + if (!frontswap_test(swap_info[swp_type(entry)], + swp_offset(entry))) + continue; + } + + indices[ret] = xas.xa_index; + entries[ret] = page; + + if (need_resched()) { + xas_pause(&xas); + cond_resched_rcu(); + } + if (++ret == nr_entries) + break; } rcu_read_unlock(); - return entry ? xas.xa_index : -1; + return ret; } /* - * If swap found in inode, free it and move page from swapcache to filecache. + * Move the swapped pages for an inode to page cache. Returns the count + * of pages swapped in, or the error in case of failure. */ -static int shmem_unuse_inode(struct shmem_inode_info *info, - swp_entry_t swap, struct page **pagep) +static int shmem_unuse_swap_entries(struct inode *inode, struct pagevec pvec, + pgoff_t *indices) { - struct address_space *mapping = info->vfs_inode.i_mapping; - void *radswap; - pgoff_t index; - gfp_t gfp; + int i = 0; + int ret = 0; int error = 0; + struct address_space *mapping = inode->i_mapping; - radswap = swp_to_radix_entry(swap); - index = find_swap_entry(&mapping->i_pages, radswap); - if (index == -1) - return -EAGAIN; /* tell shmem_unuse we found nothing */ - - /* - * Move _head_ to start search for next from here. - * But be careful: shmem_evict_inode checks list_empty without taking - * mutex, and there's an instant in list_move_tail when info->swaplist - * would appear empty, if it were the only one on shmem_swaplist. - */ - if (shmem_swaplist.next != &info->swaplist) - list_move_tail(&shmem_swaplist, &info->swaplist); + for (i = 0; i < pvec.nr; i++) { + struct page *page = pvec.pages[i]; - gfp = mapping_gfp_mask(mapping); - if (shmem_should_replace_page(*pagep, gfp)) { - mutex_unlock(&shmem_swaplist_mutex); - error = shmem_replace_page(pagep, gfp, info, index); - mutex_lock(&shmem_swaplist_mutex); - /* - * We needed to drop mutex to make that restrictive page - * allocation, but the inode might have been freed while we - * dropped it: although a racing shmem_evict_inode() cannot - * complete without emptying the page cache, our page lock - * on this swapcache page is not enough to prevent that - - * free_swap_and_cache() of our swap entry will only - * trylock_page(), removing swap from page cache whatever. - * - * We must not proceed to shmem_add_to_page_cache() if the - * inode has been freed, but of course we cannot rely on - * inode or mapping or info to check that. However, we can - * safely check if our swap entry is still in use (and here - * it can't have got reused for another page): if it's still - * in use, then the inode cannot have been freed yet, and we - * can safely proceed (if it's no longer in use, that tells - * nothing about the inode, but we don't need to unuse swap). - */ - if (!page_swapcount(*pagep)) - error = -ENOENT; + if (!xa_is_value(page)) + continue; + error = shmem_swapin_page(inode, indices[i], + &page, SGP_CACHE, + mapping_gfp_mask(mapping), + NULL, NULL); + if (error == 0) { + unlock_page(page); + put_page(page); + ret++; + } + if (error == -ENOMEM) + break; + error = 0; } + return error ? error : ret; +} - /* - * We rely on shmem_swaplist_mutex, not only to protect the swaplist, - * but also to hold up shmem_evict_inode(): so inode cannot be freed - * beneath us (pagelock doesn't help until the page is in pagecache). - */ - if (!error) - error = shmem_add_to_page_cache(*pagep, mapping, index, - radswap, gfp); - if (error != -ENOMEM) { - /* - * Truncation and eviction use free_swap_and_cache(), which - * only does trylock page: if we raced, best clean up here. - */ - delete_from_swap_cache(*pagep); - set_page_dirty(*pagep); - if (!error) { - spin_lock_irq(&info->lock); - info->swapped--; - spin_unlock_irq(&info->lock); - swap_free(swap); +/* + * If swap found in inode, free it and move page from swapcache to filecache. + */ +static int shmem_unuse_inode(struct inode *inode, unsigned int type, + bool frontswap, unsigned long *fs_pages_to_unuse) +{ + struct address_space *mapping = inode->i_mapping; + pgoff_t start = 0; + struct pagevec pvec; + pgoff_t indices[PAGEVEC_SIZE]; + bool frontswap_partial = (frontswap && *fs_pages_to_unuse > 0); + int ret = 0; + + pagevec_init(&pvec); + do { + unsigned int nr_entries = PAGEVEC_SIZE; + + if (frontswap_partial && *fs_pages_to_unuse < PAGEVEC_SIZE) + nr_entries = *fs_pages_to_unuse; + + pvec.nr = shmem_find_swap_entries(mapping, start, nr_entries, + pvec.pages, indices, + frontswap); + if (pvec.nr == 0) { + ret = 0; + break; } - } - return error; + + ret = shmem_unuse_swap_entries(inode, pvec, indices); + if (ret < 0) + break; + + if (frontswap_partial) { + *fs_pages_to_unuse -= ret; + if (*fs_pages_to_unuse == 0) { + ret = FRONTSWAP_PAGES_UNUSED; + break; + } + } + + start = indices[pvec.nr - 1]; + } while (true); + + return ret; } /* - * Search through swapped inodes to find and replace swap by page. + * Read all the shared memory data that resides in the swap + * device 'type' back into memory, so the swap device can be + * unused. */ -int shmem_unuse(swp_entry_t swap, struct page *page) +int shmem_unuse(unsigned int type, bool frontswap, + unsigned long *fs_pages_to_unuse) { - struct list_head *this, *next; - struct shmem_inode_info *info; - struct mem_cgroup *memcg; + struct shmem_inode_info *info, *next; + struct inode *inode; + struct inode *prev_inode = NULL; int error = 0; - /* - * There's a faint possibility that swap page was replaced before - * caller locked it: caller will come back later with the right page. - */ - if (unlikely(!PageSwapCache(page) || page_private(page) != swap.val)) - goto out; + if (list_empty(&shmem_swaplist)) + return 0; + + mutex_lock(&shmem_swaplist_mutex); /* - * Charge page using GFP_KERNEL while we can wait, before taking - * the shmem_swaplist_mutex which might hold up shmem_writepage(). - * Charged back to the user (not to caller) when swap account is used. + * The extra refcount on the inode is necessary to safely dereference + * p->next after re-acquiring the lock. New shmem inodes with swap + * get added to the end of the list and we will scan them all. */ - error = mem_cgroup_try_charge_delay(page, current->mm, GFP_KERNEL, - &memcg, false); - if (error) - goto out; - /* No memory allocation: swap entry occupies the slot for the page */ - error = -EAGAIN; - - mutex_lock(&shmem_swaplist_mutex); - list_for_each_safe(this, next, &shmem_swaplist) { - info = list_entry(this, struct shmem_inode_info, swaplist); - if (info->swapped) - error = shmem_unuse_inode(info, swap, &page); - else + list_for_each_entry_safe(info, next, &shmem_swaplist, swaplist) { + if (!info->swapped) { list_del_init(&info->swaplist); + continue; + } + + inode = igrab(&info->vfs_inode); + if (!inode) + continue; + + mutex_unlock(&shmem_swaplist_mutex); + if (prev_inode) + iput(prev_inode); + prev_inode = inode; + + error = shmem_unuse_inode(inode, type, frontswap, + fs_pages_to_unuse); cond_resched(); - if (error != -EAGAIN) + + mutex_lock(&shmem_swaplist_mutex); + next = list_next_entry(info, swaplist); + if (!info->swapped) + list_del_init(&info->swaplist); + if (error) break; - /* found nothing in this: move on to search the next */ } mutex_unlock(&shmem_swaplist_mutex); - if (error) { - if (error != -ENOMEM) - error = 0; - mem_cgroup_cancel_charge(page, memcg, false); - } else - mem_cgroup_commit_charge(page, memcg, true, false); -out: - unlock_page(page); - put_page(page); + if (prev_inode) + iput(prev_inode); + return error; } @@ -1329,7 +1355,7 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) */ mutex_lock(&shmem_swaplist_mutex); if (list_empty(&info->swaplist)) - list_add_tail(&info->swaplist, &shmem_swaplist); + list_add(&info->swaplist, &shmem_swaplist); if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) { spin_lock_irq(&info->lock); @@ -3886,7 +3912,8 @@ int __init shmem_init(void) return 0; } -int shmem_unuse(swp_entry_t swap, struct page *page) +int shmem_unuse(unsigned int type, bool frontswap, + unsigned long *fs_pages_to_unuse) { return 0; } diff --git a/mm/swapfile.c b/mm/swapfile.c index dbac1d49469d..6de46984d59d 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1799,44 +1799,77 @@ out_nolock: } static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long addr, unsigned long end, - swp_entry_t entry, struct page *page) + unsigned long addr, unsigned long end, + unsigned int type, bool frontswap, + unsigned long *fs_pages_to_unuse) { - pte_t swp_pte = swp_entry_to_pte(entry); + struct page *page; + swp_entry_t entry; pte_t *pte; + struct swap_info_struct *si; + unsigned long offset; int ret = 0; + volatile unsigned char *swap_map; - /* - * We don't actually need pte lock while scanning for swp_pte: since - * we hold page lock and mmap_sem, swp_pte cannot be inserted into the - * page table while we're scanning; though it could get zapped, and on - * some architectures (e.g. x86_32 with PAE) we might catch a glimpse - * of unmatched parts which look like swp_pte, so unuse_pte must - * recheck under pte lock. Scanning without pte lock lets it be - * preemptable whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE. - */ + si = swap_info[type]; pte = pte_offset_map(pmd, addr); do { - /* - * swapoff spends a _lot_ of time in this loop! - * Test inline before going to call unuse_pte. - */ - if (unlikely(pte_same_as_swp(*pte, swp_pte))) { - pte_unmap(pte); - ret = unuse_pte(vma, pmd, addr, entry, page); - if (ret) - goto out; - pte = pte_offset_map(pmd, addr); + struct vm_fault vmf; + + if (!is_swap_pte(*pte)) + continue; + + entry = pte_to_swp_entry(*pte); + if (swp_type(entry) != type) + continue; + + offset = swp_offset(entry); + if (frontswap && !frontswap_test(si, offset)) + continue; + + pte_unmap(pte); + swap_map = &si->swap_map[offset]; + vmf.vma = vma; + vmf.address = addr; + vmf.pmd = pmd; + page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE, &vmf); + if (!page) { + if (*swap_map == 0 || *swap_map == SWAP_MAP_BAD) + goto try_next; + return -ENOMEM; + } + + lock_page(page); + wait_on_page_writeback(page); + ret = unuse_pte(vma, pmd, addr, entry, page); + if (ret < 0) { + unlock_page(page); + put_page(page); + goto out; + } + + try_to_free_swap(page); + unlock_page(page); + put_page(page); + + if (*fs_pages_to_unuse && !--(*fs_pages_to_unuse)) { + ret = FRONTSWAP_PAGES_UNUSED; + goto out; } +try_next: + pte = pte_offset_map(pmd, addr); } while (pte++, addr += PAGE_SIZE, addr != end); pte_unmap(pte - 1); + + ret = 0; out: return ret; } static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud, unsigned long addr, unsigned long end, - swp_entry_t entry, struct page *page) + unsigned int type, bool frontswap, + unsigned long *fs_pages_to_unuse) { pmd_t *pmd; unsigned long next; @@ -1848,7 +1881,8 @@ static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud, next = pmd_addr_end(addr, end); if (pmd_none_or_trans_huge_or_clear_bad(pmd)) continue; - ret = unuse_pte_range(vma, pmd, addr, next, entry, page); + ret = unuse_pte_range(vma, pmd, addr, next, type, + frontswap, fs_pages_to_unuse); if (ret) return ret; } while (pmd++, addr = next, addr != end); @@ -1857,7 +1891,8 @@ static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud, static inline int unuse_pud_range(struct vm_area_struct *vma, p4d_t *p4d, unsigned long addr, unsigned long end, - swp_entry_t entry, struct page *page) + unsigned int type, bool frontswap, + unsigned long *fs_pages_to_unuse) { pud_t *pud; unsigned long next; @@ -1868,7 +1903,8 @@ static inline int unuse_pud_range(struct vm_area_struct *vma, p4d_t *p4d, next = pud_addr_end(addr, end); if (pud_none_or_clear_bad(pud)) continue; - ret = unuse_pmd_range(vma, pud, addr, next, entry, page); + ret = unuse_pmd_range(vma, pud, addr, next, type, + frontswap, fs_pages_to_unuse); if (ret) return ret; } while (pud++, addr = next, addr != end); @@ -1877,7 +1913,8 @@ static inline int unuse_pud_range(struct vm_area_struct *vma, p4d_t *p4d, static inline int unuse_p4d_range(struct vm_area_struct *vma, pgd_t *pgd, unsigned long addr, unsigned long end, - swp_entry_t entry, struct page *page) + unsigned int type, bool frontswap, + unsigned long *fs_pages_to_unuse) { p4d_t *p4d; unsigned long next; @@ -1888,78 +1925,66 @@ static inline int unuse_p4d_range(struct vm_area_struct *vma, pgd_t *pgd, next = p4d_addr_end(addr, end); if (p4d_none_or_clear_bad(p4d)) continue; - ret = unuse_pud_range(vma, p4d, addr, next, entry, page); + ret = unuse_pud_range(vma, p4d, addr, next, type, + frontswap, fs_pages_to_unuse); if (ret) return ret; } while (p4d++, addr = next, addr != end); return 0; } -static int unuse_vma(struct vm_area_struct *vma, - swp_entry_t entry, struct page *page) +static int unuse_vma(struct vm_area_struct *vma, unsigned int type, + bool frontswap, unsigned long *fs_pages_to_unuse) { pgd_t *pgd; unsigned long addr, end, next; int ret; - if (page_anon_vma(page)) { - addr = page_address_in_vma(page, vma); - if (addr == -EFAULT) - return 0; - else - end = addr + PAGE_SIZE; - } else { - addr = vma->vm_start; - end = vma->vm_end; - } + addr = vma->vm_start; + end = vma->vm_end; pgd = pgd_offset(vma->vm_mm, addr); do { next = pgd_addr_end(addr, end); if (pgd_none_or_clear_bad(pgd)) continue; - ret = unuse_p4d_range(vma, pgd, addr, next, entry, page); + ret = unuse_p4d_range(vma, pgd, addr, next, type, + frontswap, fs_pages_to_unuse); if (ret) return ret; } while (pgd++, addr = next, addr != end); return 0; } -static int unuse_mm(struct mm_struct *mm, - swp_entry_t entry, struct page *page) +static int unuse_mm(struct mm_struct *mm, unsigned int type, + bool frontswap, unsigned long *fs_pages_to_unuse) { struct vm_area_struct *vma; int ret = 0; - if (!down_read_trylock(&mm->mmap_sem)) { - /* - * Activate page so shrink_inactive_list is unlikely to unmap - * its ptes while lock is dropped, so swapoff can make progress. - */ - activate_page(page); - unlock_page(page); - down_read(&mm->mmap_sem); - lock_page(page); - } + down_read(&mm->mmap_sem); for (vma = mm->mmap; vma; vma = vma->vm_next) { - if (vma->anon_vma && (ret = unuse_vma(vma, entry, page))) - break; + if (vma->anon_vma) { + ret = unuse_vma(vma, type, frontswap, + fs_pages_to_unuse); + if (ret) + break; + } cond_resched(); } up_read(&mm->mmap_sem); - return (ret < 0)? ret: 0; + return ret; } /* * Scan swap_map (or frontswap_map if frontswap parameter is true) - * from current position to next entry still in use. - * Recycle to start on reaching the end, returning 0 when empty. + * from current position to next entry still in use. Return 0 + * if there are no inuse entries after prev till end of the map. */ static unsigned int find_next_to_unuse(struct swap_info_struct *si, unsigned int prev, bool frontswap) { - unsigned int max = si->max; - unsigned int i = prev; + unsigned int i; unsigned char count; /* @@ -1968,20 +1993,7 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si, * hits are okay, and sys_swapoff() has already prevented new * allocations from this area (while holding swap_lock). */ - for (;;) { - if (++i >= max) { - if (!prev) { - i = 0; - break; - } - /* - * No entries in use at top of swap_map, - * loop back to start and recheck there. - */ - max = prev + 1; - prev = 0; - i = 1; - } + for (i = prev + 1; i < si->max; i++) { count = READ_ONCE(si->swap_map[i]); if (count && swap_count(count) != SWAP_MAP_BAD) if (!frontswap || frontswap_test(si, i)) @@ -1989,240 +2001,121 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si, if ((i % LATENCY_LIMIT) == 0) cond_resched(); } + + if (i == si->max) + i = 0; + return i; } /* - * We completely avoid races by reading each swap page in advance, - * and then search for the process using it. All the necessary - * page table adjustments can then be made atomically. - * - * if the boolean frontswap is true, only unuse pages_to_unuse pages; + * If the boolean frontswap is true, only unuse pages_to_unuse pages; * pages_to_unuse==0 means all pages; ignored if frontswap is false */ +#define SWAP_UNUSE_MAX_TRIES 3 int try_to_unuse(unsigned int type, bool frontswap, unsigned long pages_to_unuse) { + struct mm_struct *prev_mm; + struct mm_struct *mm; + struct list_head *p; + int retval = 0; struct swap_info_struct *si = swap_info[type]; - struct mm_struct *start_mm; - volatile unsigned char *swap_map; /* swap_map is accessed without - * locking. Mark it as volatile - * to prevent compiler doing - * something odd. - */ - unsigned char swcount; struct page *page; swp_entry_t entry; - unsigned int i = 0; - int retval = 0; + unsigned int i; + int retries = 0; - /* - * When searching mms for an entry, a good strategy is to - * start at the first mm we freed the previous entry from - * (though actually we don't notice whether we or coincidence - * freed the entry). Initialize this start_mm with a hold. - * - * A simpler strategy would be to start at the last mm we - * freed the previous entry from; but that would take less - * advantage of mmlist ordering, which clusters forked mms - * together, child after parent. If we race with dup_mmap(), we - * prefer to resolve parent before child, lest we miss entries - * duplicated after we scanned child: using last mm would invert - * that. - */ - start_mm = &init_mm; - mmget(&init_mm); + if (!si->inuse_pages) + return 0; - /* - * Keep on scanning until all entries have gone. Usually, - * one pass through swap_map is enough, but not necessarily: - * there are races when an instance of an entry might be missed. - */ - while ((i = find_next_to_unuse(si, i, frontswap)) != 0) { + if (!frontswap) + pages_to_unuse = 0; + +retry: + retval = shmem_unuse(type, frontswap, &pages_to_unuse); + if (retval) + goto out; + + prev_mm = &init_mm; + mmget(prev_mm); + + spin_lock(&mmlist_lock); + p = &init_mm.mmlist; + while ((p = p->next) != &init_mm.mmlist) { if (signal_pending(current)) { retval = -EINTR; break; } - /* - * Get a page for the entry, using the existing swap - * cache page if there is one. Otherwise, get a clean - * page and read the swap into it. - */ - swap_map = &si->swap_map[i]; - entry = swp_entry(type, i); - page = read_swap_cache_async(entry, - GFP_HIGHUSER_MOVABLE, NULL, 0, false); - if (!page) { - /* - * Either swap_duplicate() failed because entry - * has been freed independently, and will not be - * reused since sys_swapoff() already disabled - * allocation from here, or alloc_page() failed. - */ - swcount = *swap_map; - /* - * We don't hold lock here, so the swap entry could be - * SWAP_MAP_BAD (when the cluster is discarding). - * Instead of fail out, We can just skip the swap - * entry because swapoff will wait for discarding - * finish anyway. - */ - if (!swcount || swcount == SWAP_MAP_BAD) - continue; - retval = -ENOMEM; - break; - } + mm = list_entry(p, struct mm_struct, mmlist); + if (!mmget_not_zero(mm)) + continue; + spin_unlock(&mmlist_lock); + mmput(prev_mm); + prev_mm = mm; + retval = unuse_mm(mm, type, frontswap, &pages_to_unuse); - /* - * Don't hold on to start_mm if it looks like exiting. - */ - if (atomic_read(&start_mm->mm_users) == 1) { - mmput(start_mm); - start_mm = &init_mm; - mmget(&init_mm); + if (retval) { + mmput(prev_mm); + goto out; } /* - * Wait for and lock page. When do_swap_page races with - * try_to_unuse, do_swap_page can handle the fault much - * faster than try_to_unuse can locate the entry. This - * apparently redundant "wait_on_page_locked" lets try_to_unuse - * defer to do_swap_page in such a case - in some tests, - * do_swap_page and try_to_unuse repeatedly compete. - */ - wait_on_page_locked(page); - wait_on_page_writeback(page); - lock_page(page); - wait_on_page_writeback(page); - - /* - * Remove all references to entry. + * Make sure that we aren't completely killing + * interactive performance. */ - swcount = *swap_map; - if (swap_count(swcount) == SWAP_MAP_SHMEM) { - retval = shmem_unuse(entry, page); - /* page has already been unlocked and released */ - if (retval < 0) - break; - continue; - } - if (swap_count(swcount) && start_mm != &init_mm) - retval = unuse_mm(start_mm, entry, page); - - if (swap_count(*swap_map)) { - int set_start_mm = (*swap_map >= swcount); - struct list_head *p = &start_mm->mmlist; - struct mm_struct *new_start_mm = start_mm; - struct mm_struct *prev_mm = start_mm; - struct mm_struct *mm; - - mmget(new_start_mm); - mmget(prev_mm); - spin_lock(&mmlist_lock); - while (swap_count(*swap_map) && !retval && - (p = p->next) != &start_mm->mmlist) { - mm = list_entry(p, struct mm_struct, mmlist); - if (!mmget_not_zero(mm)) - continue; - spin_unlock(&mmlist_lock); - mmput(prev_mm); - prev_mm = mm; + cond_resched(); + spin_lock(&mmlist_lock); + } + spin_unlock(&mmlist_lock); - cond_resched(); + mmput(prev_mm); - swcount = *swap_map; - if (!swap_count(swcount)) /* any usage ? */ - ; - else if (mm == &init_mm) - set_start_mm = 1; - else - retval = unuse_mm(mm, entry, page); - - if (set_start_mm && *swap_map < swcount) { - mmput(new_start_mm); - mmget(mm); - new_start_mm = mm; - set_start_mm = 0; - } - spin_lock(&mmlist_lock); - } - spin_unlock(&mmlist_lock); - mmput(prev_mm); - mmput(start_mm); - start_mm = new_start_mm; - } - if (retval) { - unlock_page(page); - put_page(page); - break; - } + i = 0; + while ((i = find_next_to_unuse(si, i, frontswap)) != 0) { - /* - * If a reference remains (rare), we would like to leave - * the page in the swap cache; but try_to_unmap could - * then re-duplicate the entry once we drop page lock, - * so we might loop indefinitely; also, that page could - * not be swapped out to other storage meanwhile. So: - * delete from cache even if there's another reference, - * after ensuring that the data has been saved to disk - - * since if the reference remains (rarer), it will be - * read from disk into another page. Splitting into two - * pages would be incorrect if swap supported "shared - * private" pages, but they are handled by tmpfs files. - * - * Given how unuse_vma() targets one particular offset - * in an anon_vma, once the anon_vma has been determined, - * this splitting happens to be just what is needed to - * handle where KSM pages have been swapped out: re-reading - * is unnecessarily slow, but we can fix that later on. - */ - if (swap_count(*swap_map) && - PageDirty(page) && PageSwapCache(page)) { - struct writeback_control wbc = { - .sync_mode = WB_SYNC_NONE, - }; - - swap_writepage(compound_head(page), &wbc); - lock_page(page); - wait_on_page_writeback(page); - } + entry = swp_entry(type, i); + page = find_get_page(swap_address_space(entry), i); + if (!page) + continue; /* * It is conceivable that a racing task removed this page from - * swap cache just before we acquired the page lock at the top, - * or while we dropped it in unuse_mm(). The page might even - * be back in swap cache on another swap area: that we must not - * delete, since it may not have been written out to swap yet. - */ - if (PageSwapCache(page) && - likely(page_private(page) == entry.val) && - (!PageTransCompound(page) || - !swap_page_trans_huge_swapped(si, entry))) - delete_from_swap_cache(compound_head(page)); - - /* - * So we could skip searching mms once swap count went - * to 1, we did not mark any present ptes as dirty: must - * mark page dirty so shrink_page_list will preserve it. + * swap cache just before we acquired the page lock. The page + * might even be back in swap cache on another swap area. But + * that is okay, try_to_free_swap() only removes stale pages. */ - SetPageDirty(page); + lock_page(page); + wait_on_page_writeback(page); + try_to_free_swap(page); unlock_page(page); put_page(page); /* - * Make sure that we aren't completely killing - * interactive performance. + * For frontswap, we just need to unuse pages_to_unuse, if + * it was specified. Need not check frontswap again here as + * we already zeroed out pages_to_unuse if not frontswap. */ - cond_resched(); - if (frontswap && pages_to_unuse > 0) { - if (!--pages_to_unuse) - break; - } + if (pages_to_unuse && --pages_to_unuse == 0) + goto out; } - mmput(start_mm); - return retval; + /* + * Lets check again to see if there are still swap entries in the map. + * If yes, we would need to do retry the unuse logic again. + * Under global memory pressure, swap entries can be reinserted back + * into process space after the mmlist loop above passes over them. + * Its not worth continuosuly retrying to unuse the swap in this case. + * So we try SWAP_UNUSE_MAX_TRIES times. + */ + if (++retries >= SWAP_UNUSE_MAX_TRIES) + retval = -EBUSY; + else if (si->inuse_pages) + goto retry; + +out: + return (retval == FRONTSWAP_PAGES_UNUSED) ? 0 : retval; } /* |