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[49.186.94.37]) by smtp.gmail.com with ESMTPSA id c4-20020aa781c4000000b0065da94fe917sm7379093pfn.36.2023.06.28.14.53.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jun 2023 14:53:47 -0700 (PDT) Received: from dave by dread.disaster.area with local (Exim 4.96) (envelope-from ) id 1qEd6f-00HNoi-02; Thu, 29 Jun 2023 07:53:45 +1000 Date: Thu, 29 Jun 2023 07:53:44 +1000 From: Dave Chinner To: "Matthew Wilcox (Oracle)" Cc: Andrew Morton , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jan Kara , Christoph Hellwig Subject: Re: [PATCH] writeback: Account the number of pages written back Message-ID: References: <20230628185548.981888-1-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230628185548.981888-1-willy@infradead.org> X-Stat-Signature: 84b8s6e9a7tmqatswekbtqqce4hx3zbi X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 7735540003 X-Rspam-User: X-HE-Tag: 1687989229-311101 X-HE-Meta: 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 VeicEh8q 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jun 28, 2023 at 07:55:48PM +0100, Matthew Wilcox (Oracle) wrote: > nr_to_write is a count of pages, so we need to decrease it by the number > of pages in the folio we just wrote, not by 1. Most callers specify > either LONG_MAX or 1, so are unaffected, but writeback_sb_inodes() > might end up writing 512x as many pages as it asked for. > > Fixes: 793917d997df ("mm/readahead: Add large folio readahead") > Signed-off-by: Matthew Wilcox (Oracle) > --- > mm/page-writeback.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index 1d17fb1ec863..d3f42009bb70 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -2434,6 +2434,7 @@ int write_cache_pages(struct address_space *mapping, > > for (i = 0; i < nr_folios; i++) { > struct folio *folio = fbatch.folios[i]; > + unsigned long nr; > > done_index = folio->index; > > @@ -2471,6 +2472,7 @@ int write_cache_pages(struct address_space *mapping, > > trace_wbc_writepage(wbc, inode_to_bdi(mapping->host)); > error = writepage(folio, wbc, data); > + nr = folio_nr_pages(folio); This should really be done before writepage() is called, right? By the time the writepage() returns, the folio can be unlocked, the entire write completed and the folio partially invalidated which may try to split the folio... Even if this can't happen (folio refcount is elevated, right?), it makes much more sense to me to sample the size of the folio while it is obviously locked and not going to change... Other than that, change looks good. -Dave. -- Dave Chinner david@fromorbit.com