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[70.52.229.124]) by smtp.gmail.com with ESMTPSA id ny16-20020a056214399000b005ef6128255bsm145744qvb.92.2023.04.14.15.34.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Apr 2023 15:34:58 -0700 (PDT) Date: Fri, 14 Apr 2023 18:34:57 -0400 From: Peter Xu To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, willy@infradead.org, hannes@cmpxchg.org, mhocko@suse.com, josef@toxicpanda.com, jack@suse.cz, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, michel@lespinasse.org, liam.howlett@oracle.com, jglisse@google.com, vbabka@suse.cz, minchan@google.com, dave@stgolabs.net, punit.agrawal@bytedance.com, lstoakes@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH 1/1] mm: do not increment pgfault stats when page fault handler retries Message-ID: References: <20230414175444.1837474-1-surenb@google.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BE1DE40013 X-Stat-Signature: dty8acfn6nhmtbwcc5bdibdx7jnoga77 X-HE-Tag: 1681511703-993600 X-HE-Meta: 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 FACfSuhE fv4G5JMYMP/OF/Dj4ZhBqKQCHPJk3ggkNlIJmrLze0Vox1UGfmtuQ09c/cn+rca3PlqCVF1/0oXkVdhKu0xcii10JBN3yxvJlxQLgxfHGvlpzJ9XPgMcgW3/KfsDD+ocRMIaotc+sgISufQ6AJRNCgWo4Z8NX73LxAfcGMqY06yKNINhWVkkPwQ2hc0GlAoi6fx/s33CMcKcNr+qYoZ/EfqV0XfGrQLI1+BWU/vW9sfEKnIecalat9MAiLyod+EbYJSF0UEYEiNeP6O/da23cd9vhnatqjyy5sjag4YKQKd4hvmPmgzRXKcsgdoXGwTrBHjvM+OrMW2xW1z68bq8l78JlpGJ7CEUlrdsD4d2L932XcuiTNPcXIi/zsq7LcefQ+Atw 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: Hi, Suren, On Fri, Apr 14, 2023 at 03:14:23PM -0700, Suren Baghdasaryan wrote: > > It also already ignores invalid faults: > > > > if (ret & (VM_FAULT_ERROR | VM_FAULT_RETRY)) > > return; > > Can there be a case of (!VM_FAULT_ERROR && VM_FAULT_RETRY) - basically > we need to retry but no errors happened? If so then this condition > would double-count pagefaults in such cases. If ret==VM_FAULT_RETRY it should return here already, so I assume mm_account_fault() itself is fine regarding fault retries? Note that I think "ret & (VM_FAULT_ERROR | VM_FAULT_RETRY)" above means "either ERROR or RETRY we'll skip the accounting". IMHO we should have 3 cases here: - ERROR && !RETRY error triggered of any kind - RETRY && !ERROR we need to try one more time - !RETRY && !ERROR we finished the fault I don't think ERROR & RETRY can even be set at the same time so I assume there's no option 4) - a RETRY should imply no ERROR already, even though it's still incomplete so need another attempt. Thanks, -- Peter Xu