+ mm-mmap-vma_merge-use-only-primary-pointers-for-preparing-merge.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/mmap/vma_merge: use only primary pointers for preparing merge
has been added to the -mm mm-unstable branch.  Its filename is
     mm-mmap-vma_merge-use-only-primary-pointers-for-preparing-merge.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mmap-vma_merge-use-only-primary-pointers-for-preparing-merge.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Vlastimil Babka <vbabka@suse.cz>
Subject: mm/mmap/vma_merge: use only primary pointers for preparing merge
Date: Thu, 9 Mar 2023 12:12:49 +0100

Patch series "cleanup vma_merge() and improve mergeability tests".

My initial goal here was to try making the check for vm_ops->close in
is_mergeable_vma() only be applied for vma's that would be truly removed
as part of the merge (see Patch 9).  This would then allow reverting the
quick fix d014cd7c1c35 ("mm, mremap: fix mremap() expanding for vma's with
vm_ops->close()").  This was successful enough to allow the revert (Patch
10).  Checks using can_vma_merge_before() are still pessimistic about
possible vma removal, and making them precise would probably complicate
the vma_merge() code too much.

Liam's 6.3-rc1 simplification of vma_merge() and removal of __vma_adjust()
was very much helpful in understanding the vma_merge() implementation and
especially when vma removals can happen, which is now very obvious.  While
studing the code, I've found ways to make it hopefully even more easy to
follow, so that's the patches 1-8.  That made me also notice a bug that's
now already fixed in 6.3-rc1.


This patch (of 10):

In the merging preparation part of vma_merge(), some vma pointer variables
are assigned for later execution of the merge, but also read from in the
block itself.  The code is easier follow and check against the cases
diagram in the comment if the code reads only from the "primary" vma
variables prev, mid, next instead.  No functional change.

Link: https://lkml.kernel.org/r/20230309111258.24079-1-vbabka@suse.cz
Link: https://lkml.kernel.org/r/20230309111258.24079-2-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>]
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mmap.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

--- a/mm/mmap.c~mm-mmap-vma_merge-use-only-primary-pointers-for-preparing-merge
+++ a/mm/mmap.c
@@ -963,16 +963,16 @@ struct vm_area_struct *vma_merge(struct
 	    is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL)) {
 		remove = mid;				/* case 1 */
 		vma_end = next->vm_end;
-		err = dup_anon_vma(res, remove);
+		err = dup_anon_vma(prev, mid);
 		if (mid != next) {			/* case 6 */
 			remove2 = next;
-			if (!remove->anon_vma)
-				err = dup_anon_vma(res, remove2);
+			if (!mid->anon_vma)
+				err = dup_anon_vma(prev, next);
 		}
 	} else if (merge_prev) {
 		err = 0;				/* case 2 */
 		if (mid && end > mid->vm_start) {
-			err = dup_anon_vma(res, mid);
+			err = dup_anon_vma(prev, mid);
 			if (end == mid->vm_end) {	/* case 7 */
 				remove = mid;
 			} else {			/* case 5 */
@@ -985,8 +985,8 @@ struct vm_area_struct *vma_merge(struct
 		if (prev && addr < prev->vm_end) {	/* case 4 */
 			vma_end = addr;
 			adjust = mid;
-			adj_next = -(vma->vm_end - addr);
-			err = dup_anon_vma(adjust, prev);
+			adj_next = -(prev->vm_end - addr);
+			err = dup_anon_vma(mid, prev);
 		} else {
 			vma = next;			/* case 3 */
 			vma_start = addr;
@@ -995,7 +995,7 @@ struct vm_area_struct *vma_merge(struct
 			err = 0;
 			if (mid != next) {		/* case 8 */
 				remove = mid;
-				err = dup_anon_vma(res, remove);
+				err = dup_anon_vma(next, mid);
 			}
 		}
 	}
_

Patches currently in -mm which might be from vbabka@suse.cz are

mm-page_alloc-reduce-page-alloc-free-sanity-checks.patch
mm-mmap-vma_merge-use-only-primary-pointers-for-preparing-merge.patch
mm-mmap-vma_merge-use-the-proper-vma-pointer-in-case-3.patch
mm-mmap-vma_merge-use-the-proper-vma-pointers-in-cases-1-and-6.patch
mm-mmap-vma_merge-use-the-proper-vma-pointer-in-case-4.patch
mm-mmap-vma_merge-initialize-mid-and-next-in-natural-order.patch
mm-mmap-vma_merge-set-mid-to-null-if-not-applicable.patch
mm-mmap-vma_merge-rename-adj_next-to-adj_start.patch
mm-mmap-vma_merge-convert-mergeability-checks-to-return-bool.patch
mm-mmap-start-distinguishing-if-vma-can-be-removed-in-mergeability-test.patch
mm-mremap-simplify-vma-expansion-again.patch