Re: [PATCH v2 1/1] mm: ALLOC_HIGHATOMIC flag allocation issue

[zhiguojiang]

在 2023/11/10 1:49, Andrew Morton 写道:
> On Thu,  9 Nov 2023 15:31:33 +0800 Zhiguo Jiang <justinjiang@xxxxxxxx> wrote:
>
> > Add a new bool* argument to pass return flag instead of *alloc_flags
> > and add the related comments.
> Please retain (and update) the changelog with each version of a patch.
ok，I will supplement it if there is a later version.
> For reviewers (please), here's the v1 changelog:
>
> : In case of alloc_flags contain ALLOC_HIGHATOMIC and alloc order
> : is order1/2/3/10 in rmqueue(), if pages are alloced successfully
> : from pcplist cache, and move a free pageblock 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 cache --> buddy (batch >> order) allocation migratetype
> : freelist --> buddy MIGRATE_HIGHATOMIC freelist --> buddy allocation
> : migratetype freelist.
> :
> : Due to the fact that requesting pages from the pcplist cache is faster
> : than buddy, the sequence of modifying the ALLOC_HIGHATOMIC allocation is:
> : pcplist --> buddy MIGRATE_HIGHATOMIC freelist --> buddy allocation
> : migrate freelist.
> :
> : This patch can solve the allocation failure of the Non-ALLOC_HIGHATOMIC
> : alloc_flag due to excessive pages reservations in MIGRATE_HIGHATOMIC
> : freelists.
>
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -905,7 +905,6 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
> >   #endif
> >   #define ALLOC_HIGHATOMIC	0x200 /* Allows access to MIGRATE_HIGHATOMIC */
> >   #define ALLOC_KSWAPD		0x800 /* allow waking of kswapd, __GFP_KSWAPD_RECLAIM set */
> > -#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 67cec88164b1..3c84c3e3eeb0 100755
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2854,6 +2854,11 @@ struct page *__rmqueue_pcplist(struct zone *zone, unsigned int order,
> >   			int batch = nr_pcp_alloc(pcp, zone, order);
> >   			int alloced;
> >   
> > +			/*
> > +			 * If pcplist is empty and alloc_flags is with ALLOC_HIGHATOMIC,
> > +			 * it should alloc from buddy highatomic migrate freelist firstly
> > +			 * to ensure quick and successful allocation.
> > +			 */
> >   			if (alloc_flags & ALLOC_HIGHATOMIC)
> >   				goto out;
> >   
> > @@ -2925,8 +2930,8 @@ __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,
> > -			int migratetype)
> > +			gfp_t gfp_flags, unsigned int alloc_flags,
> > +			int migratetype, bool *highatomc_allocation)
> >   {
> >   	struct page *page;
> >   
> > @@ -2938,19 +2943,33 @@ 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)) {
> > -			*alloc_flags |= ALLOC_PCPLIST;
> > +				       migratetype, alloc_flags);
> > +		if (likely(page))
> >   			goto out;
> > -		}
> >   	}
> >   
> > -	page = rmqueue_buddy(preferred_zone, zone, order, *alloc_flags,
> > +	page = rmqueue_buddy(preferred_zone, zone, order, alloc_flags,
> >   							migratetype);
> >   
> > +	/*
> > +	 * The high-order atomic allocation pageblock reserved conditions:
> > +	 *
> > +	 * If the high-order atomic allocation page is alloced from pcplist,
> > +	 * the highatomic pageblock does not need to be reserved, which can
> > +	 * void to migrate an increasing number of pages into buddy
> > +	 * MIGRATE_HIGHATOMIC freelist and lead to an increasing risk of
> > +	 * allocation failure on other buddy migrate freelists.
> > +	 *
> > +	 * If the high-order atomic allocation page is alloced from buddy
> > +	 * highatomic migrate freelist, regardless of whether the allocation
> > +	 * is successful or not, the highatomic pageblock can try to be
> > +	 * reserved.
> > +	 */
> > +	if (unlikely(alloc_flags & ALLOC_HIGHATOMIC))
> > +		*highatomc_allocation = true;
> >   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));
> > @@ -3218,6 +3237,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
> >   	struct pglist_data *last_pgdat = NULL;
> >   	bool last_pgdat_dirty_ok = false;
> >   	bool no_fallback;
> > +	bool highatomc_allocation = false;
> >   
> >   retry:
> >   	/*
> > @@ -3349,7 +3369,7 @@ 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, &highatomc_allocation);
> >   		if (page) {
> >   			prep_new_page(page, order, gfp_mask, alloc_flags);
> >   
> > @@ -3357,8 +3377,7 @@ 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) &&
> > -				unlikely(!(alloc_flags & ALLOC_PCPLIST)))
> > +			if (unlikely(highatomc_allocation))
> >   				reserve_highatomic_pageblock(page, zone);
> >   
> >   			return page;
> > --
> > 2.39.0