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Message-ID: <1ef65eb7-dfc4-45c4-99db-b29609287b56@lucifer.local>
Date: Thu, 22 Aug 2024 20:41:36 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Suren Baghdasaryan <surenb@...gle.com>,
Matthew Wilcox <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>,
sidhartha.kumar@...cle.com, Bert Karwatzki <spasswolf@....de>,
Jiri Olsa <olsajiri@...il.com>, Kees Cook <kees@...nel.org>,
"Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v7 21/21] mm/vma.h: Optimise vma_munmap_struct
On Thu, Aug 22, 2024 at 03:25:43PM GMT, Liam R. Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
>
> The vma_munmap_struct has a hole of 4 bytes and pushes the struct to
> three cachelines. Relocating the three booleans upwards allows for the
> struct to only use two cachelines (as reported by pahole on amd64).
>
> Before:
> struct vma_munmap_struct {
> struct vma_iterator * vmi; /* 0 8 */
> struct vm_area_struct * vma; /* 8 8 */
> struct vm_area_struct * prev; /* 16 8 */
> struct vm_area_struct * next; /* 24 8 */
> struct list_head * uf; /* 32 8 */
> long unsigned int start; /* 40 8 */
> long unsigned int end; /* 48 8 */
> long unsigned int unmap_start; /* 56 8 */
> /* --- cacheline 1 boundary (64 bytes) --- */
> long unsigned int unmap_end; /* 64 8 */
> int vma_count; /* 72 4 */
>
> /* XXX 4 bytes hole, try to pack */
>
> long unsigned int nr_pages; /* 80 8 */
> long unsigned int locked_vm; /* 88 8 */
> long unsigned int nr_accounted; /* 96 8 */
> long unsigned int exec_vm; /* 104 8 */
> long unsigned int stack_vm; /* 112 8 */
> long unsigned int data_vm; /* 120 8 */
> /* --- cacheline 2 boundary (128 bytes) --- */
> bool unlock; /* 128 1 */
> bool clear_ptes; /* 129 1 */
> bool closed_vm_ops; /* 130 1 */
>
> /* size: 136, cachelines: 3, members: 19 */
> /* sum members: 127, holes: 1, sum holes: 4 */
> /* padding: 5 */
> /* last cacheline: 8 bytes */
> };
>
> After:
> struct vma_munmap_struct {
> struct vma_iterator * vmi; /* 0 8 */
> struct vm_area_struct * vma; /* 8 8 */
> struct vm_area_struct * prev; /* 16 8 */
> struct vm_area_struct * next; /* 24 8 */
> struct list_head * uf; /* 32 8 */
> long unsigned int start; /* 40 8 */
> long unsigned int end; /* 48 8 */
> long unsigned int unmap_start; /* 56 8 */
> /* --- cacheline 1 boundary (64 bytes) --- */
> long unsigned int unmap_end; /* 64 8 */
> int vma_count; /* 72 4 */
> bool unlock; /* 76 1 */
> bool clear_ptes; /* 77 1 */
> bool closed_vm_ops; /* 78 1 */
>
> /* XXX 1 byte hole, try to pack */
>
> long unsigned int nr_pages; /* 80 8 */
> long unsigned int locked_vm; /* 88 8 */
> long unsigned int nr_accounted; /* 96 8 */
> long unsigned int exec_vm; /* 104 8 */
> long unsigned int stack_vm; /* 112 8 */
> long unsigned int data_vm; /* 120 8 */
>
> /* size: 128, cachelines: 2, members: 19 */
> /* sum members: 127, holes: 1, sum holes: 1 */
> };
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
> mm/vma.h | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/vma.h b/mm/vma.h
> index 7047fedce459..c774642697a0 100644
> --- a/mm/vma.h
> +++ b/mm/vma.h
> @@ -40,15 +40,16 @@ struct vma_munmap_struct {
> unsigned long unmap_start; /* Unmap PTE start */
> unsigned long unmap_end; /* Unmap PTE end */
> int vma_count; /* Number of vmas that will be removed */
> + bool unlock; /* Unlock after the munmap */
> + bool clear_ptes; /* If there are outstanding PTE to be cleared */
> + bool closed_vm_ops; /* call_mmap() was encountered, so vmas may be closed */
> + /* 1 byte hole */
> unsigned long nr_pages; /* Number of pages being removed */
> unsigned long locked_vm; /* Number of locked pages */
> unsigned long nr_accounted; /* Number of VM_ACCOUNT pages */
> unsigned long exec_vm;
> unsigned long stack_vm;
> unsigned long data_vm;
> - bool unlock; /* Unlock after the munmap */
> - bool clear_ptes; /* If there are outstanding PTE to be cleared */
> - bool closed_vm_ops; /* call_mmap() was encountered, so vmas may be closed */
> };
>
> #ifdef CONFIG_DEBUG_VM_MAPLE_TREE
> --
> 2.43.0
>
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