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X-IronPort-AV: E=McAfee;i="6500,9779,10557"; a="298042967" X-IronPort-AV: E=Sophos;i="5.96,236,1665471600"; d="scan'208";a="298042967" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Dec 2022 04:03:36 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10557"; a="754591659" X-IronPort-AV: E=Sophos;i="5.96,236,1665471600"; d="scan'208";a="754591659" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Dec 2022 04:03:34 -0800 From: "Huang, Ying" To: Kairui Song Cc: Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Miaohe Lin , David Hildenbrand , Hugh Dickins Subject: Re: [PATCH 5/5] swap: avoid ra statistic lost when swapin races References: <20221208180209.50845-1-ryncsn@gmail.com> <20221208180209.50845-6-ryncsn@gmail.com> Date: Sun, 11 Dec 2022 20:02:45 +0800 In-Reply-To: (Kairui Song's message of "Fri, 9 Dec 2022 09:54:31 +0800") Message-ID: <87edt6qhay.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 8FDE7180019 X-Stat-Signature: exiwcfgg7msowduoia7d5ixgmjxmgspr X-Rspam-User: X-HE-Tag: 1670760218-620825 X-HE-Meta: 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 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: Kairui Song writes: > Matthew Wilcox =E4=BA=8E2022=E5=B9=B412=E6=9C=889= =E6=97=A5=E5=91=A8=E4=BA=94 03:14=E5=86=99=E9=81=93=EF=BC=9A >> > > Hi, thanks for the review. > >> On Fri, Dec 09, 2022 at 02:02:09AM +0800, Kairui Song wrote: >> > From: Kairui Song >> > >> > __read_swap_cache_async should just call swap_cache_get_folio for tryi= ng >> > to look up the swap cache. Because swap_cache_get_folio handles the >> > readahead statistic, and clears the RA flag, looking up the cache >> > directly will skip these parts. >> > >> > And the comment no longer applies after commit 442701e7058b >> > ("mm/swap: remove swap_cache_info statistics"), just remove them. >> >> But what about the readahead stats? >> > > Shouldn't readahead stats be accounted here? __read_swap_cache_async > is called by swap read in path, if it hits the swap cache, and the > page have readahead page flag set, then accounting that readahead > should be just the right thing todo. And the readahead flag is checked > with folio_test_clear_readahead, so there should be no issue about > repeated accounting. > > Only the addr info of the swap_readahead_info could be updated for > multiple times by racing readers, but I think that seems fine, since > we don't know which swap read comes later in case of race, just let > the last reader that hits the swap cache update the address info of > readahead makes sense to me. > > Or do you mean I should update the comment about the readahead stat > instead of just drop the commnet? __read_swap_cache_async() is called by readahead too (swap_vma_readahead/__read_swap_cache_async). I don't think that it's a good idea to do swap readahead operation in this function. Best Regards, Huang, Ying