| Message ID | 20230208022400.28962-1-coolqyj@163.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V2] mm/filemap: fix page end in filemap_get_read_batch | expand |
On Wed, Feb 08, 2023 at 10:24:00AM +0800, coolqyj@163.com wrote: > From: Qian Yingjin <qian@ddn.com> > > 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. > > 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 > --- > mm/filemap.c | 5 +++-- > 1 file 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)) > -- > 2.34.1 >
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))