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, Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Hansen , David Hildenbrand , Mel Gorman , Vlastimil Babka , Zi Yan , Michal Hocko , Peter Zijlstra , Minchan Kim , Johannes Weiner , Hugh Dickins Subject: Re: [RFC 2/3] mm: Add a new page flag PageLayzyFree() for MADV_FREE Message-ID: <20200316223814.dpzlmfpb6a2cus25@master> Reply-To: Wei Yang References: <20200228033819.3857058-1-ying.huang@intel.com> <20200228033819.3857058-3-ying.huang@intel.com> <20200315081854.rcqlmfckeqrh7fbt@master> <92d4b0fe-f592-8da6-0282-2ea8a015b247@nextfour.com> <20200315122217.45mioaxzuulwvx2f@master> <87pnddrt5t.fsf@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87pnddrt5t.fsf@yhuang-dev.intel.com> User-Agent: NeoMutt/20170113 (1.7.2) 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 Mon, Mar 16, 2020 at 09:21:34AM +0800, Huang, Ying wrote: >Wei Yang writes: > >> On Sun, Mar 15, 2020 at 10:54:03AM +0200, Mika Penttil?? wrote: >>> >>> >>>On 15.3.2020 10.18, Wei Yang wrote: >>>> On Fri, Feb 28, 2020 at 11:38:18AM +0800, Huang, Ying wrote: >>>> > From: Huang Ying >>>> > >>>> > Now !PageSwapBacked() is used as the flag for the pages freed lazily >>>> > via MADV_FREE. This isn't obvious enough. So Dave suggested to add a >>>> > new page flag for that to improve the code readability. >>>> I am confused with the usage of PageSwapBacked(). >>>> >>>> Previously I thought this flag means the page is swapin, set in >>>> swapin_readahead(). While I found page_add_new_anon_rmap() would set it too. >>>> This means every anon page would carry this flag. Then what is this flag >>>> means? >>>> >>>> >>> >>>But not all PageSwapBacked() pages are anon, like shmem. >>> >> >> Yes, while it looks shmem is the only exception. > >Another exception is the pages freed lazily via MADV_FREE. > >> I am still struggling to understand the meaning of this flag. > >You can use `git blame` to find out the commit which introduces this >flag. Which describes why this flag is introduced. Thanks, I see the purpose is to distinguish a page: a) file backed b) or otheres This sound more clear. And now this flag is also used for MADV_FREE, which sounds a little abuse. This is the purpose of this patch to make a dedicate flag for MADV_FREE. BTW, the name, swapbacked, is a little misleading. Maybe just to me. But I can't come up with better naming. :-) > >Best Regards, >Huang, Ying > >>> >>>--Mika -- Wei Yang Help you, Help me