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Wed, 22 Mar 2023 09:06:36 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id CizrIRzFGmS1VgAAMHmgww (envelope-from ); Wed, 22 Mar 2023 09:06:36 +0000 Message-ID: Date: Wed, 22 Mar 2023 10:06:36 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH v3 2/4] mm/mmap/vma_merge: fold curr, next assignment logic Content-Language: en-US To: Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Cc: David Hildenbrand , Matthew Wilcox , "Liam R . Howlett" , maple-tree@lists.infradead.org, Vernon Yang References: <36399b6cdc843eb7fe243488ea9b29464f699170.1679468982.git.lstoakes@gmail.com> From: Vlastimil Babka In-Reply-To: <36399b6cdc843eb7fe243488ea9b29464f699170.1679468982.git.lstoakes@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 2A72B180005 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: 6napyydzoiyr87rbqws6quek3z1ryx6q X-HE-Tag: 1679475997-761703 X-HE-Meta: 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 z6q0hUTP VS1gyGcXfWGrzExxjgXpCNMKjgc6aFL/fzAOa1mACMBIuuOUUGts56vjJTKTJe3ScQWqygrG6eBjNcbRRDLKpztJnntmEnbLK3LNCqwns9V7e93ZnKK4RXKFbPvEEJ480EJR4144lxEYhBmUYmDyObruPQzlfKv7pM5h5wq43093LC6VGxQSop1gD0Ce5+sS2Da8eYHbQMHi7IjAxUdDeIJChkAdk9scu1Mps5uMkC2J9W2TqJwoMmFnBuyRLfApdBojaYEYptNF2wRdqH0+Vew8xkHofVbYiiFMx 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 3/22/23 08:13, Lorenzo Stoakes wrote: > Use find_vma_intersection() and vma_lookup() to both simplify the logic and > to fold the end == next->vm_start condition into one block. > > This groups all of the simple range checks together and establishes the > invariant that, if prev, curr or next are non-NULL then their positions are > as expected. > > This has no functional impact. I'm not so sure... > Signed-off-by: Lorenzo Stoakes > --- > mm/mmap.c | 24 +++++++++++------------- > 1 file changed, 11 insertions(+), 13 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index c9834364ac98..dbdbb92493b2 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -930,15 +930,14 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, > if (vm_flags & VM_SPECIAL) > return NULL; > > - curr = find_vma(mm, prev ? prev->vm_end : 0); > - if (curr && curr->vm_end == end) /* cases 6, 7, 8 */ > - next = find_vma(mm, curr->vm_end); > - else > - next = curr; > + /* Does the input range span an existing VMA? (cases 5 - 8) */ > + curr = find_vma_intersection(mm, prev ? prev->vm_end : 0, end); > > - /* In cases 1 - 4 there's no CCCC vma */ > - if (curr && end <= curr->vm_start) > - curr = NULL; > + if (!curr || /* cases 1 - 4 */ > + end == curr->vm_end) /* cases 6 - 8, adjacent VMA */ > + next = vma_lookup(mm, end); AFAICS if the next vma is not adjacent to CCCC or ****, but there's a gap, this will still give you a non-NULL result? > + else > + next = NULL; /* case 5 */ > > /* verify some invariant that must be enforced by the caller */ > VM_WARN_ON(prev && addr <= prev->vm_start); > @@ -959,11 +958,10 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, > } > } > /* Can we merge the successor? */ > - if (next && end == next->vm_start && And then without this end == next->vm_start check, merge will be done despite the gap. > - mpol_equal(policy, vma_policy(next)) && > - can_vma_merge_before(next, vm_flags, > - anon_vma, file, pgoff+pglen, > - vm_userfaultfd_ctx, anon_name)) { > + if (next && mpol_equal(policy, vma_policy(next)) && > + can_vma_merge_before(next, vm_flags, > + anon_vma, file, pgoff+pglen, > + vm_userfaultfd_ctx, anon_name)) { > merge_next = true; > } > > -- > 2.39.2