diff options
| author | Qian Yingjin <qian@ddn.com> | 2023-02-08 10:24:00 +0800 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-02-16 18:11:58 -0800 |
| commit | 5956592ce337330cdff0399a6f8b6a5aea397a8e (patch) | |
| tree | f3266b69e8e9db48688e526ab5efec2ed9a504ba | |
| parent | ce4d9a1ea35ac5429e822c4106cb2859d5c71f3e (diff) | |
mm/filemap: fix page end in filemap_get_read_batch
I was running traces of the read code against an RAID storage system to
understand why read requests were being misaligned against the underlying
RAID strips. I found that the page end offset calculation in
filemap_get_read_batch() was off by one.
When a read is submitted with end offset 1048575, then it calculates the
end page for read of 256 when it should be 255. "last_index" is the index
of the page beyond the end of the read and it should be skipped when get a
batch of pages for read in @filemap_get_read_batch().
The below simple patch fixes the problem. This code was introduced in
kernel 5.12.
Link: https://lkml.kernel.org/r/20230208022400.28962-1-coolqyj@163.com
Fixes: cbd59c48ae2b ("mm/filemap: use head pages in generic_file_buffered_read")
Signed-off-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | mm/filemap.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/mm/filemap.c b/mm/filemap.c index c4d4ace9cc70..0e20a8d6dd93 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2588,18 +2588,19 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter, struct folio *folio; int err = 0; + /* "last_index" is the index of the page beyond the end of the read */ last_index = DIV_ROUND_UP(iocb->ki_pos + iter->count, PAGE_SIZE); retry: if (fatal_signal_pending(current)) return -EINTR; - filemap_get_read_batch(mapping, index, last_index, fbatch); + filemap_get_read_batch(mapping, index, last_index - 1, fbatch); if (!folio_batch_count(fbatch)) { if (iocb->ki_flags & IOCB_NOIO) return -EAGAIN; page_cache_sync_readahead(mapping, ra, filp, index, last_index - index); - filemap_get_read_batch(mapping, index, last_index, fbatch); + filemap_get_read_batch(mapping, index, last_index - 1, fbatch); } if (!folio_batch_count(fbatch)) { if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ)) |