Messages in this thread | | | Date | Wed, 20 Oct 2021 12:06:19 +0100 | From | Matthew Wilcox <> | Subject | Re: [PATCH v2] mm: Stop filemap_read() from grabbing a superfluous page |
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On Wed, Oct 20, 2021 at 11:10:31AM +0100, David Howells wrote: > 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. > > Changes: > v2) Break out of the loop immediately rather than going to put_pages (the > pvec is unoccupied). Setting isize is then unnecessary. > > Signed-off-by: David Howells <dhowells@redhat.com> > cc: Kent Overstreet <kent.overstreet@gmail.com> > cc: Matthew Wilcox (Oracle) <willy@infradead.org> > cc: Andrew Morton <akpm@linux-foundation.org> > cc: Jeff Layton <jlayton@redhat.com> > 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/ > Link: https://lore.kernel.org/r/163456863216.2614702.6384850026368833133.stgit@warthog.procyon.org.uk/
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
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