在 2023/11/9 5:57, Andrew Morton 写道:
On Wed, 8 Nov 2023 14:54:07 +0800 Zhiguo Jiang <justinjiang@xxxxxxxx> wrote:
Hi Andrew Morton :
In response to your three good suggestions, I have made relevant
modifications in [PATCH v2 1/1], thanks for your review.
https://lore.kernel.org/all/20231109073133.792-2-justinjiang@xxxxxxxx/
In case that alloc_flags contains ALLOC_HIGHATOMIC and alloc order
is order1/2/3/10 in rmqueue(), if pages are alloced successfully
from pcplist, a free pageblock will be also moved from the alloced
migratetype freelist to MIGRATE_HIGHATOMIC freelist, rather than
alloc from MIGRATE_HIGHATOMIC freelist firstly, so this will result
in an increasing number of pages on the MIGRATE_HIGHATOMIC freelist,
pages in other migratetype freelist are reduced and more likely to
allocation failure.
Currently the sequence of ALLOC_HIGHATOMIC allocation is:
pcplist --> rmqueue_bulk() --> rmqueue_buddy() MIGRATE_HIGHATOMIC
--> rmqueue_buddy() allocation migratetype.
Due to the fact that requesting pages from the pcplist is faster than
buddy, the sequence of modifying the ALLOC_HIGHATOMIC allocation is:
pcplist --> rmqueue_buddy() MIGRATE_HIGHATOMIC --> rmqueue_buddy()
allocation migratetype.
This patch can solve the failure problem of allocating other types of
pages due to excessive MIGRATE_HIGHATOMIC freelist reservations.
In comparative testing, cat /proc/pagetypeinfo and the HighAtomic
freelist size is:
Test without this patch:
Node 0, zone Normal, type HighAtomic 2369 771 138 15 0 0 0 0 0 0 0
Test with this patch:
Node 0, zone Normal, type HighAtomic 206 82 4 2 1 0 0 0 0 0 0
Hopefully hannes can check this for us, but I have a stylistic concern...
+#define ALLOC_PCPLIST 0x1000 /* Allocations from pcplist */
/* Flags that allow allocations below the min watermark. */
#define ALLOC_RESERVES (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b8544f08cc36..67cec88164b1
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2854,11 +2854,15 @@ struct page *__rmqueue_pcplist(struct zone *zone, unsigned int order,
int batch = nr_pcp_alloc(pcp, zone, order);
int alloced;
+ if (alloc_flags & ALLOC_HIGHATOMIC)
+ goto out;
+
A comment here explaining why we're doing this would help readers.
add in [PATCH v2 1/1].
alloced = rmqueue_bulk(zone, order,
batch, list,
migratetype, alloc_flags);
pcp->count += alloced << order;
+out:
if (unlikely(list_empty(list)))
return NULL;
}
@@ -2921,7 +2925,7 @@ __no_sanitize_memory
static inline
struct page *rmqueue(struct zone *preferred_zone,
struct zone *zone, unsigned int order,
- gfp_t gfp_flags, unsigned int alloc_flags,
+ gfp_t gfp_flags, unsigned int *alloc_flags,
int migratetype)
{
struct page *page;
@@ -2934,17 +2938,19 @@ struct page *rmqueue(struct zone *preferred_zone,
if (likely(pcp_allowed_order(order))) {
page = rmqueue_pcplist(preferred_zone, zone, order,
- migratetype, alloc_flags);
- if (likely(page))
+ migratetype, *alloc_flags);
+ if (likely(page)) {
+ *alloc_flags |= ALLOC_PCPLIST;
goto out;
+ }
}
So we're effectively returning a boolean to the caller via *alloc_flags.
This isn't a great way of doing it. Wouldn't it be cleaner to pass a
new bool* argument to rmqueue() for this? Make it explicit?
rmqueue() will be inlined into its sole caller, so this approach
shouldn't add overhead.
Yes，I agree with your suggestion that pass a new bool* argument to
rmqueue() for this, it is more clearer.
I have modified in [PATCH v2 1/1].
- page = rmqueue_buddy(preferred_zone, zone, order, alloc_flags,
+ page = rmqueue_buddy(preferred_zone, zone, order, *alloc_flags,
migratetype);
out:
/* Separate test+clear to avoid unnecessary atomics */
- if ((alloc_flags & ALLOC_KSWAPD) &&
+ if ((*alloc_flags & ALLOC_KSWAPD) &&
unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))) {
clear_bit(ZONE_BOOSTED_WATERMARK, &zone->flags);
wakeup_kswapd(zone, 0, 0, zone_idx(zone));
@@ -3343,7 +3349,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
try_this_zone:
page = rmqueue(ac->preferred_zoneref->zone, zone, order,
- gfp_mask, alloc_flags, ac->migratetype);
+ gfp_mask, &alloc_flags, ac->migratetype);
if (page) {
prep_new_page(page, order, gfp_mask, alloc_flags);
@@ -3351,7 +3357,8 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
* If this is a high-order atomic allocation then check
* if the pageblock should be reserved for the future
*/
- if (unlikely(alloc_flags & ALLOC_HIGHATOMIC))
+ if (unlikely(alloc_flags & ALLOC_HIGHATOMIC) &&
+ unlikely(!(alloc_flags & ALLOC_PCPLIST)))
Again, a comment explaining the reason for the test would be good.
add in [PATCH v2 1/1].
reserve_highatomic_pageblock(page, zone);
return page;
--
2.39.0
