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Wed, 10 Feb 2021 07:58:51 -0800 (PST) Received: from google.com ([2620:15c:211:201:e5b0:be96:1dfb:a1f6]) by smtp.gmail.com with ESMTPSA id q2sm2431299pfu.215.2021.02.10.07.58.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Feb 2021 07:58:50 -0800 (PST) Date: Wed, 10 Feb 2021 07:58:48 -0800 From: Minchan Kim To: Vlastimil Babka Cc: Oscar Salvador , David Hildenbrand , Andrew Morton , linux-mm , LKML , Michal Hocko Subject: Re: [PATCH] mm: remove lru_add_drain_all in alloc_contig_range Message-ID: References: <20210209175048.361638-1-minchan@kernel.org> <20210209190332.GA3363@localhost.localdomain> <49491777-6d61-db4d-5e90-7a8b9045faca@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49491777-6d61-db4d-5e90-7a8b9045faca@suse.cz> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Feb 10, 2021 at 01:17:33PM +0100, Vlastimil Babka wrote: > On 2/9/21 8:03 PM, Oscar Salvador wrote: > > On Tue, Feb 09, 2021 at 07:17:59PM +0100, David Hildenbrand wrote: > >> I was expecting some magical reason why this is still required but I am not > >> able to find a compelling one. Maybe this is really some historical > >> artifact. > >> > >> Let's see if other people know why this call here still exists. > > > > I also stumbled upon this while working on adding hugetlb support for > > alloc_acontig_range [1]. > > I have to confess I puzzled me a bit. > > > > I saw it going back to when the function was first introduced by > > > > commit 041d3a8cdc18dc375a128d90bbb753949a81b1fb > > Author: Michal Nazarewicz > > Date: Thu Dec 29 13:09:50 2011 +0100 > > > > mm: page_alloc: introduce alloc_contig_range() > > > > > > It does not make much sense to me. At this point our pages are free, so > > we do not care about LRU handling here. > > But I might be missing something. > > AFAICS, at the time page migration used putback_lru_page() to release the > migration source page. This would put the page on lru pvec even if it was in > fact not mapped anywhere anymore, and only the drain would actually free it. > Seems Minchan optimized this in 2016 by c6c919eb90e0 ("mm: use put_page() to > free page instead of putback_lru_page()") > > > [1] https://lore.kernel.org/linux-mm/20210208103935.GA32103@linux/T/#md651fc6e73c656105179382f92f8b2d6073051d1 Thanks for digging history, Vlastimil!