mm: further refactor commit_merge()

The current VMA merge mechanism contains a number of confusing mechanisms
around removal of VMAs on merge and the shrinking of the VMA adjacent to
vma->target in the case of merges which result in a partial merge with
that adjacent VMA.

Since we now have a STABLE set of VMAs - prev, middle, next - we are now
able to have the caller of commit_merge() explicitly tell us which VMAs
need deleting, using newly introduced internal VMA merge flags.

Doing so allows us to embed this state within the VMG and remove the
confusing remove, remove2 parameters from commit_merge().

We additionally are able to eliminate the highly confusing and misleading
'expanded' parameter - a parameter that in reality refers to whether or
not the return VMA is the target one or the one immediately adjacent.

We can infer which is the case from whether or not the adj_start parameter
is negative.  This also allows us to simplify further logic around
iterator configuration and VMA iterator stores.

Doing so means we can also eliminate the adjust parameter, as we are able
to infer which VMA ought to be adjusted from adj_start - a positive value
implies we adjust the start of 'middle', a negative one implies we adjust
the start of 'next'.

We are then able to have commit_merge() explicitly return the target VMA,
or NULL on inability to pre-allocate memory.  Errors were previously
filtered so behaviour does not change.

We additionally move from the slightly odd use of a bitwise-flag enum
vmg->merge_flags field to vmg bitfields.

This patch has no change in functional behaviour.

Link: https://lkml.kernel.org/r/7bf2ed24af68aac18672b7acebbd9102f48c5b03.1738326519.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>

1 files changed, 7 insertions, 2 deletions

diff --git a/tools/testing/vma/vma.c b/tools/testing/vma/vma.c
index 3c0572120e94..7728498b2f7e 100644
--- a/tools/testing/vma/vma.c
+++ b/tools/testing/vma/vma.c
@@ -149,11 +149,16 @@ static void vmg_set_range(struct vma_merge_struct *vmg, unsigned long start,
 	vmg->prev = NULL;
 	vmg->middle = NULL;
 	vmg->next = NULL;
+	vmg->target = NULL;
 
 	vmg->start = start;
 	vmg->end = end;
 	vmg->pgoff = pgoff;
 	vmg->flags = flags;
+
+	vmg->just_expand = false;
+	vmg->__remove_middle = false;
+	vmg->__remove_next = false;
 }
 
 /*
@@ -1546,7 +1551,7 @@ static bool test_expand_only_mode(void)
 	/*
 	 * Place a VMA prior to the one we're expanding so we assert that we do
 	 * not erroneously try to traverse to the previous VMA even though we
-	 * have, through the use of VMG_FLAG_JUST_EXPAND, indicated we do not
+	 * have, through the use of the just_expand flag, indicated we do not
 	 * need to do so.
 	 */
 	alloc_and_link_vma(&mm, 0, 0x2000, 0, flags);
@@ -1558,7 +1563,7 @@ static bool test_expand_only_mode(void)
 	vma_iter_set(&vmi, 0x3000);
 	vma_prev = alloc_and_link_vma(&mm, 0x3000, 0x5000, 3, flags);
 	vmg.prev = vma_prev;
-	vmg.merge_flags = VMG_FLAG_JUST_EXPAND;
+	vmg.just_expand = true;
 
 	vma = vma_merge_new_range(&vmg);
 	ASSERT_NE(vma, NULL);