* [PATCH] xen/page_alloc: Don't hold the heap_lock when clearing PGC_need_scrub
@ 2021-04-06 19:30 Julien Grall
2021-04-07 9:31 ` Jan Beulich
0 siblings, 1 reply; 2+ messages in thread
From: Julien Grall @ 2021-04-06 19:30 UTC (permalink / raw)
To: xen-devel
Cc: julien, Julien Grall, Andrew Cooper, George Dunlap, Ian Jackson,
Jan Beulich, Stefano Stabellini, Wei Liu
From: Julien Grall <jgrall@amazon.com>
Currently, the heap_lock is held when clearing PGC_need_scrub in
alloc_heap_pages(). However, this is unnecessary because the only caller
(mark_page_offline()) that can concurrently modify the count_info is
using cmpxchg() in a loop.
Therefore, rework the code to avoid holding the heap_lock and use
test_and_clear_bit() instead.
Signed-off-by: Julien Grall <jgrall@amazon.com>
---
xen/common/page_alloc.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 68e47d963842..70146a00ec8b 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1038,16 +1038,12 @@ static struct page_info *alloc_heap_pages(
{
for ( i = 0; i < (1U << order); i++ )
{
- if ( test_bit(_PGC_need_scrub, &pg[i].count_info) )
+ if ( test_and_clear_bit(_PGC_need_scrub, &pg[i].count_info) )
{
if ( !(memflags & MEMF_no_scrub) )
scrub_one_page(&pg[i]);
dirty_cnt++;
-
- spin_lock(&heap_lock);
- pg[i].count_info &= ~PGC_need_scrub;
- spin_unlock(&heap_lock);
}
else if ( !(memflags & MEMF_no_scrub) )
check_one_page(&pg[i]);
--
2.17.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] xen/page_alloc: Don't hold the heap_lock when clearing PGC_need_scrub
2021-04-06 19:30 [PATCH] xen/page_alloc: Don't hold the heap_lock when clearing PGC_need_scrub Julien Grall
@ 2021-04-07 9:31 ` Jan Beulich
0 siblings, 0 replies; 2+ messages in thread
From: Jan Beulich @ 2021-04-07 9:31 UTC (permalink / raw)
To: Julien Grall
Cc: Julien Grall, Andrew Cooper, George Dunlap, Ian Jackson,
Stefano Stabellini, Wei Liu, xen-devel
On 06.04.2021 21:30, Julien Grall wrote:
> From: Julien Grall <jgrall@amazon.com>
>
> Currently, the heap_lock is held when clearing PGC_need_scrub in
> alloc_heap_pages(). However, this is unnecessary because the only caller
> (mark_page_offline()) that can concurrently modify the count_info is
> using cmpxchg() in a loop.
>
> Therefore, rework the code to avoid holding the heap_lock and use
> test_and_clear_bit() instead.
>
> Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
^ permalink raw reply [flat|nested] 2+ messages in thread
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