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Mon, 02 Nov 2020 07:19:52 -0800 (PST) Date: Mon, 2 Nov 2020 10:18:07 -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 Subject: Re: [PATCH v20 16/20] mm/compaction: do page isolation first in compaction Message-ID: <20201102151807.GI724984@cmpxchg.org> References: <1603968305-8026-1-git-send-email-alex.shi@linux.alibaba.com> <1603968305-8026-17-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: <1603968305-8026-17-git-send-email-alex.shi@linux.alibaba.com> 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 Thu, Oct 29, 2020 at 06:45:01PM +0800, Alex Shi wrote: > Currently, compaction would get the lru_lock and then do page isolation > which works fine with pgdat->lru_lock, since any page isoltion would > compete for the lru_lock. If we want to change to memcg lru_lock, we > have to isolate the page before getting lru_lock, thus isoltion would > block page's memcg change which relay on page isoltion too. Then we > could safely use per memcg lru_lock later. > > The new page isolation use previous introduced TestClearPageLRU() + > pgdat lru locking which will be changed to memcg lru lock later. > > Hugh Dickins fixed following bugs in this patch's > early version: > > Fix lots of crashes under compaction load: isolate_migratepages_block() > must clean up appropriately when rejecting a page, setting PageLRU again > if it had been cleared; and a put_page() after get_page_unless_zero() > cannot safely be done while holding locked_lruvec - it may turn out to > be the final put_page(), which will take an lruvec lock when PageLRU. > And move __isolate_lru_page_prepare back after get_page_unless_zero to > make trylock_page() safe: > trylock_page() is not safe to use at this time: its setting PG_locked > can race with the page being freed or allocated ("Bad page"), and can > also erase flags being set by one of those "sole owners" of a freshly > allocated page who use non-atomic __SetPageFlag(). > > Suggested-by: Johannes Weiner > Signed-off-by: Alex Shi > Acked-by: Hugh Dickins > Cc: Andrew Morton > Cc: Matthew Wilcox > Cc: linux-kernel@vger.kernel.org > Cc: linux-mm@kvack.org Acked-by: Johannes Weiner