Messages in this thread Patch in this message | | | Subject | [PATCH 01/67] mm: Stop filemap_read() from grabbing a superfluous page | From | David Howells <> | Date | Mon, 18 Oct 2021 15:50:32 +0100 |
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Under some circumstances, filemap_read() will allocate sufficient pages to read to the end of the file, call readahead/readpages on them and copy the data over - and then it will allocate another page at the EOF and call readpage on that and then ignore it. This is unnecessary and a waste of time and resources.
filemap_read() *does* check for this, but only after it has already done the allocation and I/O. Fix this by checking before calling filemap_get_pages() also.
Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Kent Overstreet <kent.overstreet@gmail.com> cc: Matthew Wilcox (Oracle) <willy@infradead.org> cc: linux-mm@kvack.org cc: linux-fsdevel@vger.kernel.org Link: https://lore.kernel.org/r/160588481358.3465195.16552616179674485179.stgit@warthog.procyon.org.uk/ ---
mm/filemap.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/mm/filemap.c b/mm/filemap.c index dae481293b5d..c0cdc44c844e 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2625,6 +2625,10 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter, if ((iocb->ki_flags & IOCB_WAITQ) && already_read) iocb->ki_flags |= IOCB_NOWAIT; + isize = i_size_read(inode); + if (unlikely(iocb->ki_pos >= isize)) + goto put_pages; + error = filemap_get_pages(iocb, iter, &pvec); if (error < 0) break;
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