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Tue, 10 Nov 2020 11:03:23 -0800 (PST) Date: Tue, 10 Nov 2020 14:01:36 -0500 From: Johannes Weiner To: Alex Shi Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, tj@kernel.org, hughd@google.com, khlebnikov@yandex-team.ru, daniel.m.jordan@oracle.com, willy@infradead.org, lkp@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, shakeelb@google.com, iamjoonsoo.kim@lge.com, richard.weiyang@gmail.com, kirill@shutemov.name, alexander.duyck@gmail.com, rong.a.chen@intel.com, mhocko@suse.com, vdavydov.dev@gmail.com, shy828301@gmail.com, Vlastimil Babka , Minchan Kim Subject: Re: [PATCH v21 07/19] mm: page_idle_get_page() does not need lru_lock Message-ID: <20201110190136.GD850433@cmpxchg.org> References: <1604566549-62481-1-git-send-email-alex.shi@linux.alibaba.com> <1604566549-62481-8-git-send-email-alex.shi@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1604566549-62481-8-git-send-email-alex.shi@linux.alibaba.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 05, 2020 at 04:55:37PM +0800, Alex Shi wrote: > From: Hugh Dickins > > It is necessary for page_idle_get_page() to recheck PageLRU() after > get_page_unless_zero(), but holding lru_lock around that serves no > useful purpose, and adds to lru_lock contention: delete it. > > See https://lore.kernel.org/lkml/20150504031722.GA2768@blaptop for the > discussion that led to lru_lock there; but __page_set_anon_rmap() now > uses WRITE_ONCE(), and I see no other risk in page_idle_clear_pte_refs() > using rmap_walk() (beyond the risk of racing PageAnon->PageKsm, mostly > but not entirely prevented by page_count() check in ksm.c's > write_protect_page(): that risk being shared with page_referenced() and > not helped by lru_lock). > > Signed-off-by: Hugh Dickins > Signed-off-by: Alex Shi > Cc: Andrew Morton > Cc: Vladimir Davydov > Cc: Vlastimil Babka > Cc: Minchan Kim > Cc: Alex Shi > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org Acked-by: Johannes Weiner