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mm: eliminate adj_start parameter from commit_merge()

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Introduce internal vmg->__adjust_middle_start and vmg->__adjust_next_start
merge flags, enabling us to indicate to commit_merge() that we are
performing a merge which either spans only part of vmg->middle, or part of
vmg->next respectively.

In the former instance, we change the start of vmg->middle to match the
attributes of vmg->prev, without spanning all of vmg->middle.

This implies that vmg->prev->vm_end and vmg->middle->vm_start are both
increased to form the new merged VMA (vmg->prev) and the new subsequent
VMA (vmg->middle).

In the latter case, we change the end of vmg->middle to match the
attributes of vmg->next, without spanning all of vmg->next.

This implies that vmg->middle->vm_end and vmg->next->vm_start are both
decreased to form the new merged VMA (vmg->next) and the new prior VMA
(vmg->middle).

Since we now have a stable set of prev, middle, next VMAs threaded through
vmg and with these flags set know what is happening, we can perform the
calculation in commit_merge() instead.

This allows us to drop the confusing adj_start parameter and instead pass
semantic information to commit_merge().

In the latter case the -(middle->vm_end - start) calculation becomes
-(middle->vm-end - vmg->end), however this is correct as vmg->end is set
to the start parameter.

This is because in this case (rather confusingly), we manipulate
vmg->middle, but ultimately return vmg->next, whose range will be
correctly specified.  At this point vmg->start, end is the new range for
the prior VMA rather than the merged one.

This patch has no change in functional behaviour.

Link: https://lkml.kernel.org/r/bcec0cd980b373a5eb02236cb033034ce1effe42.1738326519.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lorenzo Stoakes
2025-01-31 12:31:51 +00:00
committed by Andrew Morton
parent 6ab2d9c7c6
commit fe3e9cf0d7
4 changed files with 48 additions and 22 deletions
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8
mm/debug.c
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@@ -267,7 +267,9 @@ void dump_vmg(const struct vma_merge_struct *vmg, const char *reason)
"uffd_ctx %px\n"
"anon_name %px\n"
"state %x\n"
"just_expand %d __remove_middle %d __remove_next %d\n",
"just_expand %d\n"
"__adjust_middle_start %d __adjust_next_start %d\n"
"__remove_middle %d __remove_next %d\n",
vmg, vmg->mm, vmg->pgoff,
vmg->vmi, vmg->vmi ? vma_iter_addr(vmg->vmi) : 0,
vmg->vmi ? vma_iter_end(vmg->vmi) : 0,
@@ -281,7 +283,9 @@ void dump_vmg(const struct vma_merge_struct *vmg, const char *reason)
#endif
vmg->anon_name,
(int)vmg->state,
vmg->just_expand, vmg->__remove_middle, vmg->__remove_next);
vmg->just_expand,
vmg->__adjust_middle_start, vmg->__adjust_next_start,
vmg->__remove_middle, vmg->__remove_next);
if (vmg->mm) {
pr_warn("vmg %px mm:\n", vmg);