From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id D83106B025E for ; Fri, 20 Oct 2017 11:07:22 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id 4so1198687wrt.8 for ; Fri, 20 Oct 2017 08:07:22 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id n128sor414015wma.79.2017.10.20.08.07.21 for (Google Transport Security); Fri, 20 Oct 2017 08:07:21 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20171020061902.sqz5vklhtqrawelf@dhcp22.suse.cz> References: <20171019222507.2894-1-shakeelb@google.com> <20171020061902.sqz5vklhtqrawelf@dhcp22.suse.cz> From: Shakeel Butt Date: Fri, 20 Oct 2017 08:07:19 -0700 Message-ID: Subject: Re: [PATCH v2] mm: mlock: remove lru_add_drain_all() Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , "Kirill A. Shutemov" , Vlastimil Babka , Joonsoo Kim , Minchan Kim , Yisheng Xie , Ingo Molnar , Greg Thelen , Hugh Dickins , Balbir Singh , Anshuman Khandual , Linux MM , LKML On Thu, Oct 19, 2017 at 11:19 PM, Michal Hocko wrote: > On Thu 19-10-17 15:25:07, Shakeel Butt wrote: >> lru_add_drain_all() is not required by mlock() and it will drain >> everything that has been cached at the time mlock is called. And >> that is not really related to the memory which will be faulted in >> (and cached) and mlocked by the syscall itself. >> >> Without lru_add_drain_all() the mlocked pages can remain on pagevecs >> and be moved to evictable LRUs. However they will eventually be moved >> back to unevictable LRU by reclaim. So, we can safely remove >> lru_add_drain_all() from mlock syscall. Also there is no need for >> local lru_add_drain() as it will be called deep inside __mm_populate() >> (in follow_page_pte()). > > This paragraph can be still a bit confusing. I suspect you meant to say > something like: "If anything lru_add_drain_all" should be called _after_ > pages have been mlocked and faulted in but even that is not strictly > needed because those pages would get to the appropriate LRUs lazily > during the reclaim path. Moreover follow_page_pte (gup) will drain the > local pcp LRU cache." > Andrew, can you please replace the second paragraph of the commit with Michal's suggested paragraph. >> On larger machines the overhead of lru_add_drain_all() in mlock() can >> be significant when mlocking data already in memory. We have observed >> high latency in mlock() due to lru_add_drain_all() when the users >> were mlocking in memory tmpfs files. >> >> Signed-off-by: Shakeel Butt > > Anyway, this patch makes a lot of sense to me. Feel free to add > Acked-by: Michal Hocko > Thanks. -- 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