diff options
| author | David Hildenbrand <david@redhat.com> | 2024-03-27 15:35:48 +0100 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2024-04-25 20:56:24 -0700 |
| commit | 3b612c8f069fecb84af277c8b90e14832749ceca (patch) | |
| tree | 00c320ef0457162742cf802289fc5c267b1a379f /include | |
| parent | 07db63a2161a66a2198bc20c7580dd95af887ff4 (diff) | |
| download | lwn-3b612c8f069fecb84af277c8b90e14832749ceca.tar.gz lwn-3b612c8f069fecb84af277c8b90e14832749ceca.zip | |
mm: optimize CONFIG_PER_VMA_LOCK member placement in vm_area_struct
Currently, we end up wasting some memory in each vm_area_struct. Pahole
states that:
[...]
int vm_lock_seq; /* 40 4 */
/* XXX 4 bytes hole, try to pack */
struct vma_lock * vm_lock; /* 48 8 */
bool detached; /* 56 1 */
/* XXX 7 bytes hole, try to pack */
[...]
Let's reduce the holes and memory wastage by moving the bool:
[...]
bool detached; /* 40 1 */
/* XXX 3 bytes hole, try to pack */
int vm_lock_seq; /* 44 4 */
struct vma_lock * vm_lock; /* 48 8 */
[...]
Effectively shrinking the vm_area_struct with CONFIG_PER_VMA_LOCK by
8 byte.
Likely, we could place "detached" in the lowest bit of vm_lock, but at
least on 64bit that won't really make a difference, so keep it simple.
Link: https://lkml.kernel.org/r/20240327143548.744070-1-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/mm_types.h | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 6fef56938a17..fee6561feb7e 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -671,6 +671,9 @@ struct vm_area_struct { }; #ifdef CONFIG_PER_VMA_LOCK + /* Flag to indicate areas detached from the mm->mm_mt tree */ + bool detached; + /* * Can only be written (using WRITE_ONCE()) while holding both: * - mmap_lock (in write mode) @@ -687,9 +690,6 @@ struct vm_area_struct { */ int vm_lock_seq; struct vma_lock *vm_lock; - - /* Flag to indicate areas detached from the mm->mm_mt tree */ - bool detached; #endif /* |