The patch titled
Subject: mm: eliminate adj_start parameter from commit_merge()
has been added to the -mm mm-unstable branch. Its filename is
mm-eliminate-adj_start-parameter-from-commit_merge.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-eliminate-adj_start-parameter-from-commit_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: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Subject: mm: eliminate adj_start parameter from commit_merge()
Date: Wed, 29 Jan 2025 18:16:37 +0000
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/5a12615fc1432f353c4424ef58d4ebbda7a08b14.1738172812.git.lorenzo.stoakes@xxxxxxxxxx
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Liam Howlett <liam.howlett@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/debug.c | 8 ++++--
mm/vma.c | 50 ++++++++++++++++++++++----------------
mm/vma.h | 10 +++++++
tools/testing/vma/vma.c | 2 +
4 files changed, 48 insertions(+), 22 deletions(-)
--- a/mm/debug.c~mm-eliminate-adj_start-parameter-from-commit_merge
+++ a/mm/debug.c
@@ -267,7 +267,9 @@ void dump_vmg(const struct vma_merge_str
"uffd_ctx %px\n"
"anon_name %px\n"
"state %x\n"
- "just_expand %b __remove_middle %b __remove_next %b\n",
+ "just_expand %b\n"
+ "__adjust_middle_start %b __adjust_next_start %b\n"
+ "__remove_middle %b __remove_next %b\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_str
#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);
--- a/mm/vma.c~mm-eliminate-adj_start-parameter-from-commit_merge
+++ a/mm/vma.c
@@ -632,29 +632,44 @@ void validate_mm(struct mm_struct *mm)
*
* On success, returns the merged VMA. Otherwise returns NULL.
*/
-static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg,
- long adj_start)
+static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg)
{
- struct vma_prepare vp;
struct vm_area_struct *remove = NULL;
struct vm_area_struct *remove2 = NULL;
+ struct vma_prepare vp;
struct vm_area_struct *adjust = NULL;
+ long adj_start;
+ bool merge_target;
+
/*
- * In all cases but that of merge right, shrink next, we write
- * vmg->target to the maple tree and return this as the merged VMA.
+ * If modifying an existing VMA and we don't remove vmg->middle, then we
+ * shrink the adjacent VMA.
*/
- bool merge_target = adj_start >= 0;
+ if (vmg->__adjust_middle_start) {
+ adjust = vmg->middle;
+ /* The POSITIVE value by which we offset vmg->middle->vm_start. */
+ adj_start = vmg->end - vmg->middle->vm_start;
+ merge_target = true;
+ } else if (vmg->__adjust_next_start) {
+ adjust = vmg->next;
+ /* The NEGATIVE value by which we offset vmg->next->vm_start. */
+ adj_start = -(vmg->middle->vm_end - vmg->end);
+ /*
+ * In all cases but this - merge right, shrink next - we write
+ * vmg->target to the maple tree and return this as the merged VMA.
+ */
+ merge_target = false;
+ } else {
+ adjust = NULL;
+ adj_start = 0;
+ merge_target = true;
+ }
if (vmg->__remove_middle)
remove = vmg->middle;
if (vmg->__remove_next)
remove2 = vmg->next;
- if (adj_start > 0)
- adjust = vmg->middle;
- else if (adj_start < 0)
- adjust = vmg->next;
-
init_multi_vma_prep(&vp, vmg->target, adjust, remove, remove2);
VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
@@ -738,7 +753,6 @@ static __must_check struct vm_area_struc
bool left_side = middle && start == middle->vm_start;
bool right_side = middle && end == middle->vm_end;
int err = 0;
- long adj_start = 0;
bool merge_left, merge_right, merge_both;
mmap_assert_write_locked(vmg->mm);
@@ -858,11 +872,8 @@ static __must_check struct vm_area_struc
vmg->start = prev->vm_start;
vmg->pgoff = prev->vm_pgoff;
- /*
- * We both expand prev and shrink middle.
- */
if (!vmg->__remove_middle)
- adj_start = vmg->end - middle->vm_start;
+ vmg->__adjust_middle_start = true;
err = dup_anon_vma(prev, middle, &anon_dup);
} else { /* merge_right */
@@ -891,12 +902,11 @@ static __must_check struct vm_area_struc
* IMPORTANT: This is the ONLY case where the final
* merged VMA is NOT vmg->target, but rather vmg->next.
*/
+ vmg->__adjust_next_start = true;
vmg->target = middle;
vmg->start = middle->vm_start;
vmg->end = start;
vmg->pgoff = middle->vm_pgoff;
-
- adj_start = -(middle->vm_end - start);
}
err = dup_anon_vma(next, middle, &anon_dup);
@@ -905,7 +915,7 @@ static __must_check struct vm_area_struc
if (err)
goto abort;
- res = commit_merge(vmg, adj_start);
+ res = commit_merge(vmg);
if (!res) {
if (anon_dup)
unlink_anon_vmas(anon_dup);
@@ -1079,7 +1089,7 @@ int vma_expand(struct vma_merge_struct *
if (remove_next)
vmg->__remove_next = true;
- if (!commit_merge(vmg, 0))
+ if (!commit_merge(vmg))
goto nomem;
return 0;
--- a/mm/vma.h~mm-eliminate-adj_start-parameter-from-commit_merge
+++ a/mm/vma.h
@@ -121,6 +121,16 @@ struct vma_merge_struct {
/* Internal flags set during merge process: */
/*
+ * Internal flag indicating the merge increases vmg->middle->vm_start
+ * (and thereby, vmg->prev->vm_end).
+ */
+ bool __adjust_middle_start :1;
+ /*
+ * Internal flag indicating the merge decreases vmg->next->vm_start
+ * (and thereby, vmg->middle->vm_end).
+ */
+ bool __adjust_next_start :1;
+ /*
* Internal flag used during the merge operation to indicate we will
* remove vmg->middle.
*/
--- a/tools/testing/vma/vma.c~mm-eliminate-adj_start-parameter-from-commit_merge
+++ a/tools/testing/vma/vma.c
@@ -159,6 +159,8 @@ static void vmg_set_range(struct vma_mer
vmg->just_expand = false;
vmg->__remove_middle = false;
vmg->__remove_next = false;
+ vmg->__adjust_middle_start = false;
+ vmg->__adjust_next_start = false;
}
/*
_
Patches currently in -mm which might be from lorenzo.stoakes@xxxxxxxxxx are
mm-simplify-vma-merge-structure-and-expand-comments.patch
mm-further-refactor-commit_merge.patch
mm-eliminate-adj_start-parameter-from-commit_merge.patch
mm-make-vmg-target-consistent-and-further-simplify-commit_merge.patch
mm-completely-abstract-unnecessary-adj_start-calculation.patch
