Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751949AbdCAONy (ORCPT ); Wed, 1 Mar 2017 09:13:54 -0500 Received: from mx2.suse.de ([195.135.220.15]:44357 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751882AbdCAONt (ORCPT ); Wed, 1 Mar 2017 09:13:49 -0500 Date: Wed, 1 Mar 2017 14:36:24 +0100 From: Michal Hocko To: Shaohua Li Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Kernel-team@fb.com, minchan@kernel.org, hughd@google.com, hannes@cmpxchg.org, riel@redhat.com, mgorman@techsingularity.net, akpm@linux-foundation.org Subject: Re: [PATCH V5 6/6] proc: show MADV_FREE pages info in smaps Message-ID: <20170301133624.GF1124@dhcp22.suse.cz> References: <89efde633559de1ec07444f2ef0f4963a97a2ce8.1487965799.git.shli@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <89efde633559de1ec07444f2ef0f4963a97a2ce8.1487965799.git.shli@fb.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1652 Lines: 46 On Fri 24-02-17 13:31:49, Shaohua Li wrote: > show MADV_FREE pages info of each vma in smaps. The interface is for > diganose or monitoring purpose, userspace could use it to understand > what happens in the application. Since userspace could dirty MADV_FREE > pages without notice from kernel, this interface is the only place we > can get accurate accounting info about MADV_FREE pages. I have just got to test this patchset and noticed something that was a bit surprising madvise(mmap(len), len, MADV_FREE) Size: 102400 kB Rss: 102400 kB Pss: 102400 kB Shared_Clean: 0 kB Shared_Dirty: 0 kB Private_Clean: 102400 kB Private_Dirty: 0 kB Referenced: 0 kB Anonymous: 102400 kB LazyFree: 102368 kB It took me a some time to realize that LazyFree is not accurate because there are still pages on the per-cpu lru_lazyfree_pvecs. I believe this is an implementation detail which shouldn't be visible to the userspace. Should we simply drain the pagevec? A crude way would be to simply lru_add_drain_all after we are done with the given range. We can also make this lru_lazyfree_pvecs specific but I am not sure this is worth the additional code. --- diff --git a/mm/madvise.c b/mm/madvise.c index dc5927c812d3..d2c318db16c9 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -474,7 +474,7 @@ static int madvise_free_single_vma(struct vm_area_struct *vma, madvise_free_page_range(&tlb, vma, start, end); mmu_notifier_invalidate_range_end(mm, start, end); tlb_finish_mmu(&tlb, start, end); - + lru_add_drain_all(); return 0; } -- Michal Hocko SUSE Labs