| Message ID | 20240327143548.744070-1-david@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v1] mm: optimize CONFIG_PER_VMA_LOCK member placement in vm_area_struct | expand |
On Wed, Mar 27, 2024 at 7:36 AM David Hildenbrand <david@redhat.com> wrote: > > 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. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Suren Baghdasaryan <surenb@google.com> > Signed-off-by: David Hildenbrand <david@redhat.com> Looks reasonable to me. Thanks! > --- > include/linux/mm_types.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 4ae4684d1add..f56739dece7a 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 > > /* > -- > 2.43.2 >
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 4ae4684d1add..f56739dece7a 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 /*
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. Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: David Hildenbrand <david@redhat.com> --- include/linux/mm_types.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)