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Mon, 20 Mar 2023 07:25:39 -0700 (PDT) Date: Mon, 20 Mar 2023 22:25:11 +0800 From: Vernon Yang To: Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , Matthew Wilcox , Vlastimil Babka , "Liam R . Howlett" , maple-tree@lists.infradead.org Subject: Re: [PATCH 2/4] mm/mmap/vma_merge: set next to NULL if not applicable Message-ID: References: <4d717269303d8a6fe1d837968c252eeb6ff1d7e5.1679137163.git.lstoakes@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4d717269303d8a6fe1d837968c252eeb6ff1d7e5.1679137163.git.lstoakes@gmail.com> X-Rspamd-Queue-Id: 44DEFC000C X-Stat-Signature: ib1ekbah3z5ioszj7ujgfznqgk5nf38u X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1679322341-331016 X-HE-Meta: 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 a7hoL2/T 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 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 Sat, Mar 18, 2023 at 11:13:19AM +0000, Lorenzo Stoakes wrote: > We are only interested in next if end == next->vm_start (in which case we > check to see if we can set merge_next), so perform this check alongside > checking whether curr should be set. > > 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. > > Additionally, use the abstract 'vma' object to look up the possible curr or > next VMA in order to avoid any confusion as to what these variables > represent - now curr and next are assigned once and only once. Hi Lorenzo, Due to the "vma" variable is used as an intermediate member, I feels a bit confusing, so cleanup this patch as below. If this cleanup patch is issue, please let me know, and then ignore it directly, thanks. ---- >From 7dac3ed8c1b747c2edf2a6c867c4e6342c7447c3 Mon Sep 17 00:00:00 2001 From: Vernon Yang Date: Mon, 20 Mar 2023 21:38:09 +0800 Subject: [PATCH] mm/mmap/vma_merge: set next to NULL if not applicable-cleanup Make code logic simpler and more readable. Signed-off-by: Vernon Yang --- mm/mmap.c | 23 ++++++----------------- 1 file changed, 6 insertions(+), 17 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 45bd43225013..78cb96774602 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -921,7 +921,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, * If there is a previous VMA specified, find the next, otherwise find * the first. */ - vma = find_vma(mm, prev ? prev->vm_end : 0); + curr = find_vma(mm, prev ? prev->vm_end : 0); /* * Does the input range span an existing VMA? If so, we designate this @@ -929,21 +929,19 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, * * Cases 5 - 8. */ - if (vma && end > vma->vm_start) { - curr = vma; - + if (curr && end > curr->vm_start) { /* * If the addr - end range spans this VMA entirely, then we * check to see if another VMA follows it. * - * If it is _immediately_ adjacent (checked below), then we + * If it is immediately adjacent (checked below), then we * designate it 'next' (cases 6 - 8). */ if (curr->vm_end == end) - vma = find_vma(mm, curr->vm_end); + next = find_vma(mm, curr->vm_end); else /* Case 5. */ - vma = NULL; + next = NULL; } else { /* * The addr - end range either spans the end of prev or spans no @@ -952,19 +950,10 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, * * Cases 1 - 4. */ + next = curr; curr = NULL; } - /* - * We only actually examine the next VMA if it is immediately adjacent - * to end which sits either at the end of a hole (cases 1 - 3), PPPP - * (case 4) or CCCC (cases 6 - 8). - */ - if (vma && end == vma->vm_start) - next = vma; - else - next = NULL; - /* * By default, we return prev. Cases 3, 4, 8 will instead return next * and cases 3, 8 will also update vma to point at next. -- 2.34.1 > > This has no functional impact. > > Signed-off-by: Lorenzo Stoakes > --- > mm/mmap.c | 61 ++++++++++++++++++++++++++++++++++++++++++++----------- > 1 file changed, 49 insertions(+), 12 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index c9834364ac98..66893fc72e03 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -930,15 +930,53 @@ 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; > + /* > + * If there is a previous VMA specified, find the next, otherwise find > + * the first. > + */ > + vma = find_vma(mm, prev ? prev->vm_end : 0); > + > + /* > + * Does the input range span an existing VMA? If so, we designate this > + * VMA 'curr'. The caller will have ensured that curr->vm_start == addr. > + * > + * Cases 5 - 8. > + */ > + if (vma && end > vma->vm_start) { > + curr = vma; > > - /* In cases 1 - 4 there's no CCCC vma */ > - if (curr && end <= curr->vm_start) > + /* > + * If the addr - end range spans this VMA entirely, then we > + * check to see if another VMA follows it. > + * > + * If it is _immediately_ adjacent (checked below), then we > + * designate it 'next' (cases 6 - 8). > + */ > + if (curr->vm_end == end) > + vma = find_vma(mm, curr->vm_end); > + else > + /* Case 5. */ > + vma = NULL; > + } else { > + /* > + * The addr - end range either spans the end of prev or spans no > + * VMA at all - in either case we dispense with 'curr' and > + * maintain only 'prev' and (possibly) 'next'. > + * > + * Cases 1 - 4. > + */ > curr = NULL; > + } > + > + /* > + * We only actually examine the next VMA if it is immediately adjacent > + * to end which sits either at the end of a hole (cases 1 - 3), PPPP > + * (case 4) or CCCC (cases 6 - 8). > + */ > + if (vma && end == vma->vm_start) > + next = vma; > + else > + next = NULL; > > /* verify some invariant that must be enforced by the caller */ > VM_WARN_ON(prev && addr <= prev->vm_start); > @@ -959,11 +997,10 @@ 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 && > - 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 >