Re: [PATCH v2 15/33] mm/vma: refactor vmg_adjust_set_range() for clarity
From: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>
Date: 2026-07-15 14:49:45
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damon, dri-devel, kvm, linux-arm-msm, linux-fsdevel, linux-iommu, linux-mm, linux-perf-users, linux-tegra, lkml, nvdimm
On 7/10/26 22:16, Lorenzo Stoakes wrote:
Add comments with ASCII diagrams to describe what we're doing, avoid dubious use of PHYS_PFN(), and use vma_start_pgoff(). The most complicated scenario represented here is vmg->__adjust_next_start - when this is set, vmg->[start, end] actually indicate the range to be retained, so take special care to describe this accurately. No functional change intended. Reviewed-by: Pedro Falcato <pfalcato@suse.de> Reviewed-by: Gregory Price <gourry@gourry.net> Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
quoted hunk ↗ jump to hunk
--- mm/vma.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 47 insertions(+), 4 deletions(-)diff --git a/mm/vma.c b/mm/vma.c index 084afdf37385..7265a054cfa3 100644 --- a/mm/vma.c +++ b/mm/vma.c@@ -704,11 +704,54 @@ static void vmg_adjust_set_range(struct vma_merge_struct *vmg) pgoff_t pgoff; if (vmg->__adjust_middle_start) { - adjust = vmg->middle; - pgoff = adjust->vm_pgoff + PHYS_PFN(vmg->end - adjust->vm_start); + /* + * vmg->start vmg->end + * | | + * v merge v + * <-------------> + * delta + * <------> + * |------|----------------| + * | prev | middle | + * |------|----------------| + * ^ + * | + * middle->vm_start + */ + struct vm_area_struct *middle = vmg->middle; + const unsigned long delta = vmg->end - middle->vm_start; + + pgoff = vma_start_pgoff(middle) + (delta >> PAGE_SHIFT); + adjust = middle; } else if (vmg->__adjust_next_start) { - adjust = vmg->next; - pgoff = adjust->vm_pgoff - PHYS_PFN(adjust->vm_start - vmg->end); + /* + * Originally: + * + * vmg->start vmg->end + * | | + * v merge v + * <------------> + * . . + * merge_existing_range() updates to: + * . . + * vmg->start vmg->end . + * | | . + * v retain v . + * <----------> . + * delta . + * <-----> . + * |----------------|------| + * | middle | next | + * |----------------|------| + * ^ + * | + * next->vm_start + */ + struct vm_area_struct *next = vmg->next; + const unsigned long delta = next->vm_start - vmg->end; + + pgoff = vma_start_pgoff(next) - (delta >> PAGE_SHIFT); + adjust = next; } else { return; }