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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pnNtf-008xzE-Pa; Fri, 14 Apr 2023 18:11:43 +0000 Date: Fri, 14 Apr 2023 19:11:43 +0100 From: Matthew Wilcox To: Suren Baghdasaryan Cc: 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 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 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230414175444.1837474-1-surenb@google.com> X-Rspamd-Queue-Id: BC3B8140019 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: 4pw76a7m8zttz4exhmma6by1imh1waip X-HE-Tag: 1681495931-225870 X-HE-Meta: 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 1T2rLdr+ xKvd1IQ3U5X4VCjXT/7EDxkhcOI+qwFg/jn2rxal72NY09waBSDLqWxsrIENwrGsnEsPQVOkKlbdeh/Nc8nVxEYwAd48xXjvzsmukRRlX2G4Brl5r3ViJhy6momlpyAVU8ySF3j50X4tSjwtldAfoHifIlXaD3F5PXhcWAQkJziTTP66wmkoyCMBBaSdplCT0Ofe+/9dgIxAeikKevThIgrL4nL5GBuubdqKdnOgxo/nXyA8= 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 Fri, Apr 14, 2023 at 10:54:44AM -0700, Suren Baghdasaryan wrote: > If the page fault handler requests a retry, we will count the fault > multiple times. This is a relatively harmless problem as the retry paths > are not often requested, and the only user-visible problem is that the > fault counter will be slightly higher than it should be. Nevertheless, > userspace only took one fault, and should not see the fact that the > kernel had to retry the fault multiple times. > > Fixes: 6b4c9f446981 ("filemap: drop the mmap_sem for all blocking operations") I know I suggested this fixes line, but I think it's actually been here much longer, perhaps since Fixes: d065bd810b6d ("mm: retry page fault when blocking on disk transfer") Michel, what do you think? > Signed-off-by: Suren Baghdasaryan > Reviewed-by: Matthew Wilcox (Oracle) > --- > Patch applies cleanly over linux-next and mm-unstable > > mm/memory.c | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 1c5b231fe6e3..d88f370eacd1 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5212,17 +5212,16 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address, > > __set_current_state(TASK_RUNNING); > > - count_vm_event(PGFAULT); > - count_memcg_event_mm(vma->vm_mm, PGFAULT); > - > ret = sanitize_fault_flags(vma, &flags); > if (ret) > - return ret; > + goto out; > > if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE, > flags & FAULT_FLAG_INSTRUCTION, > - flags & FAULT_FLAG_REMOTE)) > - return VM_FAULT_SIGSEGV; > + flags & FAULT_FLAG_REMOTE)) { > + ret = VM_FAULT_SIGSEGV; > + goto out; > + } > > /* > * Enable the memcg OOM handling for faults triggered in user > @@ -5253,6 +5252,11 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address, > } > > mm_account_fault(regs, address, flags, ret); > +out: > + if (!(ret & VM_FAULT_RETRY)) { > + count_vm_event(PGFAULT); > + count_memcg_event_mm(vma->vm_mm, PGFAULT); > + } > > return ret; > } > -- > 2.40.0.634.g4ca3ef3211-goog >