diff options
| author | Lorenzo Stoakes <lorenzo.stoakes@oracle.com> | 2025-11-18 10:17:46 +0000 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-11-20 13:43:58 -0800 |
| commit | 64212ba02e66e705cabce188453ba4e61e9d7325 (patch) | |
| tree | 1df334479f18f1c9e877aa96061b6a7a4dee7f88 /mm/vma.h | |
| parent | 9119d6c2095bb20292cb9812dd70d37f17e3bd37 (diff) | |
| download | tip-64212ba02e66e705cabce188453ba4e61e9d7325.tar.gz | |
mm: implement sticky VMA flags
It is useful to be able to designate that certain flags are 'sticky', that
is, if two VMAs are merged one with a flag of this nature and one without,
the merged VMA sets this flag.
As a result we ignore these flags for the purposes of determining VMA flag
differences between VMAs being considered for merge.
This patch therefore updates the VMA merge logic to perform this action,
with flags possessing this property being described in the VM_STICKY
bitmap.
Those flags which ought to be ignored for the purposes of VMA merge are
described in the VM_IGNORE_MERGE bitmap, which the VMA merge logic is also
updated to use.
As part of this change we place VM_SOFTDIRTY in VM_IGNORE_MERGE as it
already had this behaviour, alongside VM_STICKY as sticky flags by
implication must not disallow merge.
Ultimately it seems that we should make VM_SOFTDIRTY a sticky flag in its
own right, but this change is out of scope for this series.
The only sticky flag designated as such is VM_MAYBE_GUARD, so as a result
of this change, once the VMA flag is set upon guard region installation,
VMAs with guard ranges will now not have their merge behaviour impacted as
a result and can be freely merged with other VMAs without VM_MAYBE_GUARD
set.
Also update the comments for vma_modify_flags() to directly reference
sticky flags now we have established the concept.
We also update the VMA userland tests to account for the changes.
Link: https://lkml.kernel.org/r/22ad5269f7669d62afb42ce0c79bad70b994c58d.1763460113.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/vma.h')
| -rw-r--r-- | mm/vma.h | 10 |
1 files changed, 4 insertions, 6 deletions
diff --git a/mm/vma.h b/mm/vma.h index 75f1d9c7204bc5..abada6a64c4e65 100644 --- a/mm/vma.h +++ b/mm/vma.h @@ -273,17 +273,15 @@ void unmap_region(struct ma_state *mas, struct vm_area_struct *vma, * @start: The start of the range to update. May be offset within @vma. * @end: The exclusive end of the range to update, may be offset within @vma. * @vm_flags_ptr: A pointer to the VMA flags that the @start to @end range is - * about to be set to. On merge, this will be updated to include any additional - * flags which remain in place. + * about to be set to. On merge, this will be updated to include sticky flags. * * IMPORTANT: The actual modification being requested here is NOT applied, * rather the VMA is perhaps split, perhaps merged to accommodate the change, * and the caller is expected to perform the actual modification. * - * In order to account for VMA flags which may persist (e.g. soft-dirty), the - * @vm_flags_ptr parameter points to the requested flags which are then updated - * so the caller, should they overwrite any existing flags, correctly retains - * these. + * In order to account for sticky VMA flags, the @vm_flags_ptr parameter points + * to the requested flags which are then updated so the caller, should they + * overwrite any existing flags, correctly retains these. * * Returns: A VMA which contains the range @start to @end ready to have its * flags altered to *@vm_flags. |