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Thu, 18 Mar 2021 08:19:15 -0700 (PDT) Received: from google.com ([2620:15c:211:201:913d:5573:c956:f033]) by smtp.gmail.com with ESMTPSA id m21sm2816641pff.61.2021.03.18.08.19.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Mar 2021 08:19:14 -0700 (PDT) Date: Thu, 18 Mar 2021 08:19:12 -0700 From: Minchan Kim To: Shakeel Butt Cc: Heiko Carstens , Andrew Morton , Roman Gushchin , Johannes Weiner , Hugh Dickins , Juergen Christ , Christian Borntraeger , Vasily Gorbik , Linux MM , Linux-Next Mailing List Subject: Re: [BUG -next] "memcg: charge before adding to swapcache on swapin" broken Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1BD30C001C66 X-Stat-Signature: uw79omksoinhgttnmfwzegik38znron5 Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf22; identity=mailfrom; envelope-from=""; helo=mail-pf1-f170.google.com; client-ip=209.85.210.170 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616080756-89772 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000015, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Mar 17, 2021 at 06:49:27PM -0700, Shakeel Butt wrote: > On Wed, Mar 17, 2021 at 6:31 PM Minchan Kim wrote: > > > [...] > > > > > > The simplest solution I can think of is to do set_page_private(page, > > > entry.val) before swap_readpage(page, true) and set_page_private(page, > > > 0) after. > > > > Since I did't read the bug in detail, I couldn't come up with how the > > missing reset is connected the problem while missing set_page_private > > with entry.val is clear. > > This particular bug is about missing set_page_private(page, > entry.val). I was wondering if we should always reset page->private or > just leave it as is? I think it is safer to reset. For safeness point of view, I couldn't find something wrong since page_private will be used once the page turns out PageSwapCache. (please chime in if someone found) Having said, I agree it would be more consistent and safer.