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Message-ID: <164549983736.9187.16755913785880819183.stgit@noble.brown> Date: Tue, 22 Feb 2022 14:17:17 +1100 From: NeilBrown <neilb@...e.de> To: Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>, Wu Fengguang <fengguang.wu@...el.com>, Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>, Jeff Layton <jlayton@...nel.org>, Ilya Dryomov <idryomov@...il.com>, Miklos Szeredi <miklos@...redi.hu>, Trond Myklebust <trond.myklebust@...merspace.com>, Anna Schumaker <anna.schumaker@...app.com>, Ryusuke Konishi <konishi.ryusuke@...il.com>, "Darrick J. Wong" <djwong@...nel.org>, Philipp Reisner <philipp.reisner@...bit.com>, Lars Ellenberg <lars.ellenberg@...bit.com>, Paolo Valente <paolo.valente@...aro.org>, Jens Axboe <axboe@...nel.dk> Cc: linux-doc@...r.kernel.org, linux-mm@...ck.org, linux-nilfs@...r.kernel.org, linux-nfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, linux-ext4@...r.kernel.org, ceph-devel@...r.kernel.org, drbd-dev@...ts.linbit.com, linux-kernel@...r.kernel.org Subject: [PATCH 03/11] MM: improve cleanup when ->readpages doesn't process all pages. If ->readpages doesn't process all the pages, then it is best to act as though they weren't requested so that a subsequent readahead can try again. So: - remove any 'ahead' pages from the page cache so they can be loaded with ->readahead() rather then multiple ->read()s - update the file_ra_state to reflect the reads that were actually submitted. This allows ->readpages() to abort early due e.g. to congestion, which will then allow us to remove the inode_read_congested() test from page_Cache_async_ra(). Signed-off-by: NeilBrown <neilb@...e.de> --- mm/readahead.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/mm/readahead.c b/mm/readahead.c index 73b2bc5302e0..8a97bd408cf6 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -104,7 +104,13 @@ * for necessary resources (e.g. memory or indexing information) to * become available. Pages in the final ``async_size`` may be * considered less urgent and failure to read them is more acceptable. - * They will eventually be read individually using ->readpage(). + * In this case it is best to use delete_from_page_cache() to remove the + * pages from the page cache as is automatically done for pages that + * were not fetched with readahead_page(). This will allow a + * subsequent synchronous read ahead request to try them again. If they + * are left in the page cache, then they will be read individually using + * ->readpage(). + * */ #include <linux/kernel.h> @@ -226,8 +232,17 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages, if (aops->readahead) { aops->readahead(rac); - /* Clean up the remaining pages */ + /* + * Clean up the remaining pages. The sizes in ->ra + * maybe be used to size next read-ahead, so make sure + * they accurately reflect what happened. + */ while ((page = readahead_page(rac))) { + rac->ra->size -= 1; + if (rac->ra->async_size > 0) { + rac->ra->async_size -= 1; + delete_from_page_cache(page); + } unlock_page(page); put_page(page); }
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