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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1poXhb-00Bks9-Ts; Mon, 17 Apr 2023 22:52:03 +0000 Date: Mon, 17 Apr 2023 23:52:03 +0100 From: Matthew Wilcox To: Peter Xu Cc: Suren Baghdasaryan , akpm@linux-foundation.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 v2 1/1] mm: do not increment pgfault stats when page fault handler retries Message-ID: References: <20230415000818.1955007-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 368E7A000F X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: ty5bsz64coj17qm41xjw1fkri4aj3n5t X-HE-Tag: 1681771947-244617 X-HE-Meta: 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 zH/Fk5zg Ql9qKioQYEd5vSItWyMhK1JZedaoktc4blA08m1qfz2VzxEdWzhC+an71KgNygx5PNB7hCRE7B80qh5bKsLgb3pItU2O66yIUKsN9hTOIUKo6qATy1Ox9stt4KITdOpuo8F4qStQFJYBsk7xGHNcRXzLncSBNUyM41Pxg 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, Apr 17, 2023 at 03:40:33PM -0400, Peter Xu wrote: > > /* > > - * We don't do accounting for some specific faults: > > - * > > - * - Unsuccessful faults (e.g. when the address wasn't valid). That > > - * includes arch_vma_access_permitted() failing before reaching here. > > - * So this is not a "this many hardware page faults" counter. We > > - * should use the hw profiling for that. > > - * > > - * - Incomplete faults (VM_FAULT_RETRY). They will only be counted > > - * once they're completed. > > + * Do not account for incomplete faults (VM_FAULT_RETRY). They will be > > + * counted upon completion. > > */ > > - if (ret & (VM_FAULT_ERROR | VM_FAULT_RETRY)) > > + if (ret & VM_FAULT_RETRY) > > + return; > > + > > + /* Register both successful and failed faults in PGFAULT counters. */ > > + count_vm_event(PGFAULT); > > + count_memcg_event_mm(mm, PGFAULT); > > Is there reason on why vm events accountings need to be explicitly > different from perf events right below on handling ERROR? I think so. ERROR is quite different from RETRY. If we are, for example, handling a SIGSEGV (perhaps a GC language?) that should be accounted. If we can't handle a page fault right now, and need to retry within the kernel, that should not be accounted.