The patch titled
Subject: mm: optimize CONFIG_PER_VMA_LOCK member placement in vm_area_struct
has been added to the -mm mm-unstable branch. Its filename is
mm-optimize-config_per_vma_lock-member-placement-in-vm_area_struct.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-optimize-config_per_vma_lock-member-placement-in-vm_area_struct.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: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm: optimize CONFIG_PER_VMA_LOCK member placement in vm_area_struct
Date: Wed, 27 Mar 2024 15:35:48 +0100
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@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm_types.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/include/linux/mm_types.h~mm-optimize-config_per_vma_lock-member-placement-in-vm_area_struct
+++ a/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
/*
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-secretmem-fix-gup-fast-succeeding-on-secretmem-folios.patch
mm-madvise-make-madv_populate_readwrite-handle-vm_fault_retry-properly.patch
mm-madvise-dont-perform-madvise-vma-walk-for-madv_populate_readwrite.patch
mm-userfaultfd-dont-place-zeropages-when-zeropages-are-disallowed.patch
s390-mm-re-enable-the-shared-zeropage-for-pv-and-skeys-kvm-guests.patch
mm-convert-folio_estimated_sharers-to-folio_likely_mapped_shared.patch
mm-convert-folio_estimated_sharers-to-folio_likely_mapped_shared-fix.patch
selftests-memfd_secret-add-vmsplice-test.patch
mm-merge-folio_is_secretmem-and-folio_fast_pin_allowed-into-gup_fast_folio_allowed.patch
mm-optimize-config_per_vma_lock-member-placement-in-vm_area_struct.patch
