From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id 5A4076B0033 for ; Mon, 30 Oct 2017 05:12:51 -0400 (EDT) Received: by mail-pg0-f69.google.com with SMTP id y5so12991881pgq.15 for ; Mon, 30 Oct 2017 02:12:51 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id a10si9702796pgf.48.2017.10.30.02.12.49 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 30 Oct 2017 02:12:50 -0700 (PDT) Subject: Re: [PATCH v2] mm: mlock: remove lru_add_drain_all() References: <20171019222507.2894-1-shakeelb@google.com> From: Vlastimil Babka Message-ID: Date: Mon, 30 Oct 2017 10:12:46 +0100 MIME-Version: 1.0 In-Reply-To: <20171019222507.2894-1-shakeelb@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Shakeel Butt , Andrew Morton , "Kirill A. Shutemov" , Michal Hocko , Joonsoo Kim , Minchan Kim , Yisheng Xie , Ingo Molnar , Greg Thelen , Hugh Dickins Cc: Balbir Singh , Anshuman Khandual , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 10/20/2017 12:25 AM, 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()). > > 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 Acked-by: Vlastimil Babka > --- > Changelog since v1: > - updated commit message > > mm/mlock.c | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/mm/mlock.c b/mm/mlock.c > index dfc6f1912176..3ceb2935d1e0 100644 > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -669,8 +669,6 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla > if (!can_do_mlock()) > return -EPERM; > > - lru_add_drain_all(); /* flush pagevec */ > - > len = PAGE_ALIGN(len + (offset_in_page(start))); > start &= PAGE_MASK; > > @@ -797,9 +795,6 @@ SYSCALL_DEFINE1(mlockall, int, flags) > if (!can_do_mlock()) > return -EPERM; > > - if (flags & MCL_CURRENT) > - lru_add_drain_all(); /* flush pagevec */ > - > lock_limit = rlimit(RLIMIT_MEMLOCK); > lock_limit >>= PAGE_SHIFT; > > -- 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