* [PATCH] mremap: skip page table lookup for non-faulted anonymous VMAs
@ 2011-11-07 4:21 ` Nai Xia
0 siblings, 0 replies; 6+ messages in thread
From: Nai Xia @ 2011-11-07 4:21 UTC (permalink / raw)
To: Andrea Arcangeli
Cc: Hugh Dickins, Mel Gorman, Pawel Sikora, Andrew Morton, linux-mm,
jpiszcz, arekm, linux-kernel
If an anonymous vma has not yet been faulted, move_page_tables() in move_vma()
is not necessary for it.
Signed-off-by: Nai Xia <nai.xia@gmail.com>
---
diff --git a/mm/mremap.c b/mm/mremap.c
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -200,6 +200,10 @@ static unsigned long move_vma(struct vm_area_struct *vma,
if (!new_vma)
return -ENOMEM;
+ /* An anonymous vma has not been faulted, no pagetables lookup. */
+ if (!vma->vm_file && !vma->anon_vma)
+ goto page_tables_ok;
+
moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len);
if (moved_len < old_len) {
/*
@@ -213,6 +217,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
old_addr = new_addr;
new_addr = -ENOMEM;
}
+page_tables_ok:
/* Conceal VM_ACCOUNT so old reservation is not undone */
if (vm_flags & VM_ACCOUNT) {
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH] mremap: skip page table lookup for non-faulted anonymous VMAs
@ 2011-11-07 4:21 ` Nai Xia
0 siblings, 0 replies; 6+ messages in thread
From: Nai Xia @ 2011-11-07 4:21 UTC (permalink / raw)
To: Andrea Arcangeli
Cc: Hugh Dickins, Mel Gorman, Pawel Sikora, Andrew Morton, linux-mm,
jpiszcz, arekm, linux-kernel
If an anonymous vma has not yet been faulted, move_page_tables() in move_vma()
is not necessary for it.
Signed-off-by: Nai Xia <nai.xia@gmail.com>
---
diff --git a/mm/mremap.c b/mm/mremap.c
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -200,6 +200,10 @@ static unsigned long move_vma(struct vm_area_struct *vma,
if (!new_vma)
return -ENOMEM;
+ /* An anonymous vma has not been faulted, no pagetables lookup. */
+ if (!vma->vm_file && !vma->anon_vma)
+ goto page_tables_ok;
+
moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len);
if (moved_len < old_len) {
/*
@@ -213,6 +217,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
old_addr = new_addr;
new_addr = -ENOMEM;
}
+page_tables_ok:
/* Conceal VM_ACCOUNT so old reservation is not undone */
if (vm_flags & VM_ACCOUNT) {
--
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^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] mremap: skip page table lookup for non-faulted anonymous VMAs
2011-11-07 4:21 ` Nai Xia
@ 2011-11-07 15:32 ` Andrea Arcangeli
-1 siblings, 0 replies; 6+ messages in thread
From: Andrea Arcangeli @ 2011-11-07 15:32 UTC (permalink / raw)
To: Nai Xia
Cc: Hugh Dickins, Mel Gorman, Pawel Sikora, Andrew Morton, linux-mm,
jpiszcz, arekm, linux-kernel
On Mon, Nov 07, 2011 at 12:21:35PM +0800, Nai Xia wrote:
> If an anonymous vma has not yet been faulted, move_page_tables() in move_vma()
> is not necessary for it.
I actually thought of adding that (in fact fork has it and it's more
likely to be beneficial for fork than for mremap I suspect), but this
adds a branch to the fast path for a case that shouldn't normally
materialize. So I don't think it's worth adding it as I expect it to
add overhead in average.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] mremap: skip page table lookup for non-faulted anonymous VMAs
@ 2011-11-07 15:32 ` Andrea Arcangeli
0 siblings, 0 replies; 6+ messages in thread
From: Andrea Arcangeli @ 2011-11-07 15:32 UTC (permalink / raw)
To: Nai Xia
Cc: Hugh Dickins, Mel Gorman, Pawel Sikora, Andrew Morton, linux-mm,
jpiszcz, arekm, linux-kernel
On Mon, Nov 07, 2011 at 12:21:35PM +0800, Nai Xia wrote:
> If an anonymous vma has not yet been faulted, move_page_tables() in move_vma()
> is not necessary for it.
I actually thought of adding that (in fact fork has it and it's more
likely to be beneficial for fork than for mremap I suspect), but this
adds a branch to the fast path for a case that shouldn't normally
materialize. So I don't think it's worth adding it as I expect it to
add overhead in average.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
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Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] mremap: skip page table lookup for non-faulted anonymous VMAs
2011-11-07 15:32 ` Andrea Arcangeli
@ 2011-11-07 16:13 ` Nai Xia
-1 siblings, 0 replies; 6+ messages in thread
From: Nai Xia @ 2011-11-07 16:13 UTC (permalink / raw)
To: Andrea Arcangeli
Cc: Hugh Dickins, Mel Gorman, Pawel Sikora, Andrew Morton, linux-mm,
jpiszcz, arekm, linux-kernel
On Mon, Nov 7, 2011 at 11:32 PM, Andrea Arcangeli <aarcange@redhat.com> wrote:
> On Mon, Nov 07, 2011 at 12:21:35PM +0800, Nai Xia wrote:
>> If an anonymous vma has not yet been faulted, move_page_tables() in move_vma()
>> is not necessary for it.
>
> I actually thought of adding that (in fact fork has it and it's more
> likely to be beneficial for fork than for mremap I suspect), but this
> adds a branch to the fast path for a case that shouldn't normally
> materialize. So I don't think it's worth adding it as I expect it to
> add overhead in average.
>
Well, it seems like I forgot to embrace it with unlikely(), with instr
prefetching this line seems a trivial even for the average cases.
But in case it really materializes, it may avoid tedious page table
locking and pmd allocation and furthermore, a semantically
confusing operation of move_page_tables() on a same VMA.
Anyway, it's not a big deal, indeed. You are the maintainers,
it's left for you to decide.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] mremap: skip page table lookup for non-faulted anonymous VMAs
@ 2011-11-07 16:13 ` Nai Xia
0 siblings, 0 replies; 6+ messages in thread
From: Nai Xia @ 2011-11-07 16:13 UTC (permalink / raw)
To: Andrea Arcangeli
Cc: Hugh Dickins, Mel Gorman, Pawel Sikora, Andrew Morton, linux-mm,
jpiszcz, arekm, linux-kernel
On Mon, Nov 7, 2011 at 11:32 PM, Andrea Arcangeli <aarcange@redhat.com> wrote:
> On Mon, Nov 07, 2011 at 12:21:35PM +0800, Nai Xia wrote:
>> If an anonymous vma has not yet been faulted, move_page_tables() in move_vma()
>> is not necessary for it.
>
> I actually thought of adding that (in fact fork has it and it's more
> likely to be beneficial for fork than for mremap I suspect), but this
> adds a branch to the fast path for a case that shouldn't normally
> materialize. So I don't think it's worth adding it as I expect it to
> add overhead in average.
>
Well, it seems like I forgot to embrace it with unlikely(), with instr
prefetching this line seems a trivial even for the average cases.
But in case it really materializes, it may avoid tedious page table
locking and pmd allocation and furthermore, a semantically
confusing operation of move_page_tables() on a same VMA.
Anyway, it's not a big deal, indeed. You are the maintainers,
it's left for you to decide.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2011-11-07 16:13 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2011-11-07 4:21 [PATCH] mremap: skip page table lookup for non-faulted anonymous VMAs Nai Xia
2011-11-07 4:21 ` Nai Xia
2011-11-07 15:32 ` Andrea Arcangeli
2011-11-07 15:32 ` Andrea Arcangeli
2011-11-07 16:13 ` Nai Xia
2011-11-07 16:13 ` Nai Xia
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