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[70.44.39.90]) by smtp.gmail.com with ESMTPSA id p12sm2428519qtw.27.2021.02.10.16.33.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Feb 2021 16:33:01 -0800 (PST) Date: Wed, 10 Feb 2021 19:33:00 -0500 From: Johannes Weiner To: Shakeel Butt Cc: Hugh Dickins , Andrew Morton , Michal Hocko , Roman Gushchin , Linux MM , Cgroups , LKML , Kernel Team , Arjun Roy Subject: Re: [PATCH v2] mm: page-writeback: simplify memcg handling in test_clear_page_writeback() Message-ID: References: <20210209214543.112655-1-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 10, 2021 at 02:59:32PM -0800, Shakeel Butt wrote: > On Wed, Feb 10, 2021 at 9:44 AM Johannes Weiner wrote: > > From 5bcc0f468460aa2670c40318bb657e8b08ef96d5 Mon Sep 17 00:00:00 2001 > > From: Johannes Weiner > > Date: Tue, 9 Feb 2021 16:22:42 -0500 > > Subject: [PATCH] mm: page-writeback: simplify memcg handling in > > test_clear_page_writeback() > > > > Page writeback doesn't hold a page reference, which allows truncate to > > free a page the second PageWriteback is cleared. This used to require > > special attention in test_clear_page_writeback(), where we had to be > > careful not to rely on the unstable page->memcg binding and look up > > all the necessary information before clearing the writeback flag. > > > > Since commit 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and > > BUG_ON(PageWriteback)") test_clear_page_writeback() is called with an > > explicit reference on the page, and this dance is no longer needed. > > > > Use unlock_page_memcg() and dec_lruvec_page_state() directly. > > > > This removes the last user of the lock_page_memcg() return value, > > change it to void. Touch up the comments in there as well. This also > > removes the last extern user of __unlock_page_memcg(), make it > > static. Further, it removes the last user of dec_lruvec_state(), > > delete it, along with a few other unused helpers. > > > > Signed-off-by: Johannes Weiner > > Acked-by: Hugh Dickins > > Reviewed-by: Shakeel Butt > > The patch looks fine. I don't want to spoil the fun but just wanted to > call out that I might bring back __unlock_page_memcg() for the memcg > accounting of zero copy TCP memory work where we are uncharging the > page in page_remove_rmap(). That shouldn't be an issue. Just add it back if/when you need it and we have a legitimate in-tree user for it again. It still helps to remove it now; if someboy later goes through the git log to identify dependencies, they'll find your patch adding it and can stop looking. Thanks for the review!