From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Weiner Subject: Re: [PATCH v4 3/9] mm/lru: replace pgdat lru_lock with lruvec lock Date: Fri, 22 Nov 2019 11:16:52 -0500 Message-ID: <20191122161652.GA489821@cmpxchg.org> References: <1574166203-151975-1-git-send-email-alex.shi@linux.alibaba.com> <1574166203-151975-4-git-send-email-alex.shi@linux.alibaba.com> <20191119160456.GD382712@cmpxchg.org> <20191121220613.GB487872@cmpxchg.org> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=wfrcrjX2H8D8RSvVc5LOIPsNb3WQnwmD64TJNBPNLUA=; b=2CxFAF9vQ8BbOhqPOkf+HBDvDUxib+UWq9hNW0Tg4l/6YvGcIgULwb7zDfm9mbuP/9 3/EKpUXrSdv8B03hy14QpNLhWat83HNQyn1GgIfaBTMQMmmanUe+btbssVaH8haWbOpr QqRPK10O9tUUfndkbGrdfQe1z6ITlCczduG7UJhZ6JNU7ZoQRSrIbazx85Z8h4rz26Xb 6EJVTX6A/tEz9L4CMMWPjveLs+QHDUyDxvybrIHm+D9wpJ2bnJSnESNPWmTfEoXJTO6d RHERX6f1D2fDaO/gYzRlAdEHF6PJxDPr/jbgCMQMh3Z2Fj6YG7Q5lbEYKwW7Ol6/bl7e sgEw== Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="utf-8" To: Alex Shi Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, mgorman@techsingularity.net, tj@kernel.org, hughd@google.com, khlebnikov@yandex-team.ru, daniel.m.jordan@oracle.com, yang.shi@linux.alibaba.com, willy@infradead.org, shakeelb@google.com, Michal Hocko , Vladimir Davydov , Roman Gushchin , Chris Down , Thomas Gleixner , Vlastimil Babka , Qian Cai , Andrey Ryabinin , "Kirill A. Shutemov" , =?iso-8859-1?B?Suly9G1l?= Glisse , Andrea Arcangeli , David Rientjes , Aneesh Ku On Fri, Nov 22, 2019 at 10:36:32AM +0800, Alex Shi wrote: > 在 2019/11/22 上午6:06, Johannes Weiner 写道: > > If we could restrict lock_page_lruvec() to working only on PageLRU > > pages, we could fix the problem with memory barriers. But this won't > > work for split_huge_page(), which is AFAICT the only user that needs > > to freeze the lru state of a page that could be isolated elsewhere. > > > > So AFAICS the only option is to lock out mem_cgroup_move_account() > > entirely when the lru_lock is held. Which I guess should be fine. > > I guess we can try from lock_page_memcg, is that a good start? Yes. > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 7e6387ad01f0..f4bbbf72c5b8 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1224,7 +1224,7 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd > goto out; > } > > - memcg = page->mem_cgroup; > + memcg = lock_page_memcg(page); > /* > * Swapcache readahead pages are added to the LRU - and > * possibly migrated - before they are charged. test_clear_page_writeback() calls this function with that lock already held so that would deadlock. Let's keep locking in lock_page_lruvec(). lock_page_lruvec(): memcg = lock_page_memcg(page); lruvec = mem_cgroup_lruvec(page_pgdat(page), memcg); spin_lock_irqsave(&lruvec->lru_lock, *flags); return lruvec; unlock_lruvec(); spin_unlock_irqrestore(&lruvec->lru_lock); __unlock_page_memcg(lruvec_memcg(lruvec)); The lock ordering should be fine as well. But it might be a good idea to stick a might_lock(&memcg->move_lock) in lock_page_memcg() before that atomic_read() and test with lockdep enabled. But that leaves me with one more worry: compaction. We locked out charge moving now, so between that and knowing that the page is alive, we have page->mem_cgroup stable. But compaction doesn't know whether the page is alive - it comes from a pfn and finds out using PageLRU. In the current code, pgdat->lru_lock remains the same before and after the page is charged to a cgroup, so once compaction has that locked and it observes PageLRU, it can go ahead and isolate the page. But lruvec->lru_lock changes during charging, and then compaction may hold the wrong lock during isolation: compaction: generic_file_buffered_read: page_cache_alloc() !PageBuddy() lock_page_lruvec(page) lruvec = mem_cgroup_page_lruvec() spin_lock(&lruvec->lru_lock) if lruvec != mem_cgroup_page_lruvec() goto again add_to_page_cache_lru() mem_cgroup_commit_charge() page->mem_cgroup = foo lru_cache_add() __pagevec_lru_add() SetPageLRU() if PageLRU(page): __isolate_lru_page() I don't see what prevents the lruvec from changing under compaction, neither in your patches nor in Hugh's. Maybe I'm missing something?