From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f197.google.com (mail-io0-f197.google.com [209.85.223.197]) by kanga.kvack.org (Postfix) with ESMTP id BC5A36B038B for ; Wed, 1 Mar 2017 12:37:27 -0500 (EST) Received: by mail-io0-f197.google.com with SMTP id f84so51461982ioj.6 for ; Wed, 01 Mar 2017 09:37:27 -0800 (PST) Received: from mx0a-00082601.pphosted.com (mx0b-00082601.pphosted.com. [67.231.153.30]) by mx.google.com with ESMTPS id q199si5372374iod.178.2017.03.01.09.37.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 01 Mar 2017 09:37:27 -0800 (PST) Date: Wed, 1 Mar 2017 09:37:10 -0800 From: Shaohua Li Subject: Re: [PATCH V5 6/6] proc: show MADV_FREE pages info in smaps Message-ID: <20170301173710.GA12867@shli-mbp.local> References: <89efde633559de1ec07444f2ef0f4963a97a2ce8.1487965799.git.shli@fb.com> <20170301133624.GF1124@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20170301133624.GF1124@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko 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 On Wed, Mar 01, 2017 at 02:36:24PM +0100, Michal Hocko wrote: > 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. Minchan's original patch includes a drain of pvec. I discard it because I think it's not worth the effort. There aren't too many memory in the per-cpu vecs. Like what you said, I doubt this is noticeable to userspace. Thanks, Shaohua > --- > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org