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mm: refactor of vma_merge() 

Patch series "Refactor of vma_merge and new merge call", v4.

I am currently working on my master's thesis trying to increase number of
merges of VMAs currently failing because of page offset incompatibility
and difference in their anon_vmas.  The following refactor and added merge
call included in this series is just two smaller upgrades I created along
the way.


This patch (of 2):

Refactor vma_merge() to make it shorter and more understandable.  Main
change is the elimination of code duplicity in the case of merge next
check.  This is done by first doing checks and caching the results before
executing the merge itself.  The variable 'area' is divided into 'mid' and
'res' as previously it was used for two purposes, as the middle VMA
between prev and next and also as the result of the merge itself.  Exit
paths are also unified.

Link: https://lkml.kernel.org/r/20220603145719.1012094-1-matenajakub@gmail.com
Link: https://lkml.kernel.org/r/20220603145719.1012094-2-matenajakub@gmail.com
Signed-off-by: Jakub Matěna <matenajakub@gmail.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Rik van Riel <riel@surriel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Jakub Matěna 2022-06-03 16:57:18 +02:00 committed by Andrew Morton
parent b3541d912a
commit eef199440d
1 changed files with 37 additions and 50 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

87
mm/mmap.c
View File

@ -1005,8 +1005,10 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
struct anon_vma_name *anon_name)
{
pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
struct vm_area_struct *area, *next;
int err;
struct vm_area_struct *mid, *next, *res;
int err = -1;
bool merge_prev = false;
bool merge_next = false;
/*
* We later require that vma->vm_flags == vm_flags,
@ -1016,75 +1018,60 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
return NULL;
next = find_vma(mm, prev ? prev->vm_end : 0);
area = next;
if (area && area->vm_end == end) /* cases 6, 7, 8 */
mid = next;
if (next && next->vm_end == end) /* cases 6, 7, 8 */
next = find_vma(mm, next->vm_end);
/* verify some invariant that must be enforced by the caller */
VM_WARN_ON(prev && addr <= prev->vm_start);
VM_WARN_ON(area && end > area->vm_end);
VM_WARN_ON(mid && end > mid->vm_end);
VM_WARN_ON(addr >= end);
/*
* Can it merge with the predecessor?
*/
/* Can we merge the predecessor? */
if (prev && prev->vm_end == addr &&
mpol_equal(vma_policy(prev), policy) &&
can_vma_merge_after(prev, vm_flags,
anon_vma, file, pgoff,
vm_userfaultfd_ctx, anon_name)) {
/*
* OK, it can. Can we now merge in the successor as well?
*/
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) &&
is_mergeable_anon_vma(prev->anon_vma,
next->anon_vma, NULL)) {
/* cases 1, 6 */
err = __vma_adjust(prev, prev->vm_start,
next->vm_end, prev->vm_pgoff, NULL,
prev);
} else /* cases 2, 5, 7 */
err = __vma_adjust(prev, prev->vm_start,
end, prev->vm_pgoff, NULL, prev);
if (err)
return NULL;
khugepaged_enter_vma(prev, vm_flags);
return prev;
merge_prev = true;
}
/*
* Can this new request be merged in front of next?
*/
/* 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)) {
merge_next = true;
}
/* Can we merge both the predecessor and the successor? */
if (merge_prev && merge_next &&
is_mergeable_anon_vma(prev->anon_vma,
next->anon_vma, NULL)) { /* cases 1, 6 */
err = __vma_adjust(prev, prev->vm_start,
next->vm_end, prev->vm_pgoff, NULL,
prev);
res = prev;
} else if (merge_prev) { /* cases 2, 5, 7 */
err = __vma_adjust(prev, prev->vm_start,
end, prev->vm_pgoff, NULL, prev);
res = prev;
} else if (merge_next) {
if (prev && addr < prev->vm_end) /* case 4 */
err = __vma_adjust(prev, prev->vm_start,
addr, prev->vm_pgoff, NULL, next);
else { /* cases 3, 8 */
err = __vma_adjust(area, addr, next->vm_end,
next->vm_pgoff - pglen, NULL, next);
/*
* In case 3 area is already equal to next and
* this is a noop, but in case 8 "area" has
* been removed and next was expanded over it.
*/
area = next;
}
if (err)
return NULL;
khugepaged_enter_vma(area, vm_flags);
return area;
addr, prev->vm_pgoff, NULL, next);
else /* cases 3, 8 */
err = __vma_adjust(mid, addr, next->vm_end,
next->vm_pgoff - pglen, NULL, next);
res = next;
}
return NULL;
/*
* Cannot merge with predecessor or successor or error in __vma_adjust?
*/
if (err)
return NULL;
khugepaged_enter_vma(res, vm_flags);
return res;
}
/*