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AJvYcCWm0Qa1ckrY7caNKRLlJUqRmlnBqznQgFX9bMM26yO9SehEpNYnTT2IUfO7DA7mmGCvvhGFmd/ugw==@kvack.org X-Gm-Message-State: AOJu0YxVN7DHubJmxkKnlGL6hjOcYVvIiyNn3ZPgEOWI/mmUhFi3/sf6 rqMza+vyECo4qmwZPDowAK6LsW66KNWlvm0SL6DiXbvhuiH6pf5O X-Google-Smtp-Source: AGHT+IEOoCXiizsEeMxwr8Yv9vmC7pyoZDSLYksTU1WqGMSIgtjinZnuLWf4rspMHPKU+YWK8vqlmw== X-Received: by 2002:a05:6402:3550:b0:5cb:6712:6089 with SMTP id 4fb4d7f45d1cf-5cba23f1ba5mr975034a12.7.1729761013725; Thu, 24 Oct 2024 02:10:13 -0700 (PDT) Received: from localhost ([185.92.221.13]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5cb6696b68fsm5450385a12.1.2024.10.24.02.10.12 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Thu, 24 Oct 2024 02:10:13 -0700 (PDT) Date: Thu, 24 Oct 2024 09:10:12 +0000 From: Wei Yang To: Lorenzo Stoakes Cc: Wei Yang , akpm@linux-foundation.org, vbabka@suse.cz, jannh@google.com, linux-mm@kvack.org Subject: Re: [PATCH] mm/vma: the pgoff is correct if can_merge_right Message-ID: <20241024091012.52f2pugeaxd4xrul@master> Reply-To: Wei Yang References: <20241024084222.17201-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 5FAA918000C X-Stat-Signature: h51y1etffz39r99d36z9s4tgbiw6hnh3 X-Rspam-User: X-HE-Tag: 1729761002-27872 X-HE-Meta: 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 ciDidLFG 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000004, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Oct 24, 2024 at 10:03:34AM +0100, Lorenzo Stoakes wrote: >On Thu, Oct 24, 2024 at 08:42:22AM +0000, Wei Yang wrote: >> can_merge_right implies can_vma_merge_right() has checked the pgoff. >> >> Don't need to assign it again. > >Would prefer a bigger commit message something like: > >By this point can_vma_merge_right() must have returned true, which implies >can_vma_merge_before() also returned true, which already asserts that the >pgoff is as expected for a merge with the following VMA, thus this >assignment is redundant. > Will change to this in next version. >> >> Signed-off-by: Wei Yang > >Reviewed-by: Lorenzo Stoakes > >> CC: Lorenzo Stoakes >> --- >> mm/vma.c | 2 -- >> 1 file changed, 2 deletions(-) >> >> diff --git a/mm/vma.c b/mm/vma.c >> index 4737afcb064c..fb4f1863f88e 100644 >> --- a/mm/vma.c >> +++ b/mm/vma.c >> @@ -915,7 +915,6 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) >> unsigned long start = vmg->start; >> unsigned long end = vmg->end; >> pgoff_t pgoff = vmg->pgoff; >> - pgoff_t pglen = PHYS_PFN(end - start); >> bool can_merge_left, can_merge_right; >> >> mmap_assert_write_locked(vmg->mm); >> @@ -936,7 +935,6 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) >> if (can_merge_right) { >> vmg->end = next->vm_end; >> vmg->vma = next; >> - vmg->pgoff = next->vm_pgoff - pglen; >> } >> >> /* If we can merge with the previous VMA, adjust vmg accordingly. */ >> -- >> 2.34.1 >> >> > >Thanks, nice spot! > >For the purposes of explaining it on-list this is because: > >static bool can_vma_merge_right(struct vma_merge_struct *vmg, > bool can_merge_left) >{ > if (!vmg->next || vmg->end != vmg->next->vm_start || > !can_vma_merge_before(vmg)) > return false; > ... >} > >And: > >static bool can_vma_merge_before(struct vma_merge_struct *vmg) >{ > pgoff_t pglen = PHYS_PFN(vmg->end - vmg->start); >... > if (vmg->next->vm_pgoff == vmg->pgoff + pglen) > return true; >... >} > >Which implies vmg->pgoff == vmg->next->vm_pgoff - pglen. > >None of these values are changed between the check and prior assignment, so >this was an entirely redundant assignment. Do you suggest me to add this in change log? -- Wei Yang Help you, Help me