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Wed, 22 Feb 2023 09:06:21 -0800 (PST) Received: from localhost ([2620:10d:c091:480::1:5e17]) by smtp.gmail.com with ESMTPSA id a186-20020a3798c3000000b0073b878e3f30sm2751844qke.59.2023.02.22.09.06.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Feb 2023 09:06:20 -0800 (PST) Date: Wed, 22 Feb 2023 12:06:20 -0500 From: Johannes Weiner To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Yang Shi , David Stevens , stable@vger.kernel.org Subject: Re: [PATCH] mm/khugepaged: alloc_charge_hpage() take care of mem charge errors Message-ID: References: <20230221214344.609226-1-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230221214344.609226-1-peterx@redhat.com> X-Rspam-User: X-Rspamd-Queue-Id: 5695E1C001D X-Rspamd-Server: rspam01 X-Stat-Signature: rycwnxuzywxpbi6bu8iehjnipfi5tznz X-HE-Tag: 1677085582-766909 X-HE-Meta: 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 huN6F2cg n8W/stE+8o28IYrv8rK2Box5aX4ZgPtxhlqtznZ5UzotzOjeMFIYJyz6lewZDBzIP3gKhvSfbB8KTgPB7Rhn3l8IrLUGE4pPDiNdeKDn8ww0LRcPEj0f31bGo1Jif1InI3vjMhfwfda6H/ecgPBBRPYk/Sem7OSOrNLiBfIFAOhddrFobLtALqmwepeX9ypJ/+9OcfSWmhH5RFeikL7DCE0CjsBflx2KBQFlzygKxkG5eLxpsgZS89uJFNljONHAsNhvC4Q2L020xYUl1+uk177SjLMoG/IfLqAFZQC2MW1AYjcW4Vj/5QIQwGDuG90zrYcyLa4oMFLWCIf/N5PmFHC84+FHEJyVKfky4+hPNiNNUgzR/nwhjbWXyLBeCNPprvqMlTciwCHdQS49ZcruKLFyViADX1FyIAxUcXFAY17FbJtgtPMh1Havnpi4It1zbVlqOAtkNnWyrMPI= 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: Hello, On Tue, Feb 21, 2023 at 04:43:44PM -0500, Peter Xu wrote: > If memory charge failed, the caller shouldn't call mem_cgroup_uncharge(). > Let alloc_charge_hpage() handle the error itself and clear hpage properly > if mem charge fails. I'm a bit confused by this patch. There isn't anything wrong with calling mem_cgroup_uncharge() on an uncharged page, functionally. It checks and bails out. It's an unnecessary call of course, but since it's an error path it's also not a cost issue, either. I could see an argument for improving the code, but this is actually more code, and the caller still has the uncharge-and-put branch anyway for when the collapse fails later on. So I'm not sure I understand the benefit of this change.