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Date: Thu, 16 Jul 2020 16:27:09 +0900
From: Joonsoo Kim <js1304@...il.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Linux Memory Management List <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>, kernel-team@....com,
Christoph Hellwig <hch@...radead.org>,
Roman Gushchin <guro@...com>,
Mike Kravetz <mike.kravetz@...cle.com>,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Michal Hocko <mhocko@...e.com>,
"Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/4] mm/page_alloc: fix non cma alloc context
2020년 7월 15일 (수) 오후 5:24, Vlastimil Babka <vbabka@...e.cz>님이 작성:
>
> On 7/15/20 7:05 AM, js1304@...il.com wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@....com>
> >
> > Currently, preventing cma area in page allocation is implemented by using
> > current_gfp_context(). However, there are two problems of this
> > implementation.
> >
> > First, this doesn't work for allocation fastpath. In the fastpath,
> > original gfp_mask is used since current_gfp_context() is introduced in
> > order to control reclaim and it is on slowpath.
> > Second, clearing __GFP_MOVABLE has a side effect to exclude the memory
> > on the ZONE_MOVABLE for allocation target.
> >
> > To fix these problems, this patch changes the implementation to exclude
> > cma area in page allocation. Main point of this change is using the
> > alloc_flags. alloc_flags is mainly used to control allocation so it fits
> > for excluding cma area in allocation.
>
> Agreed, should have been done with ALLOC_CMA since the beginning.
>
> > Fixes: d7fefcc (mm/cma: add PF flag to force non cma alloc)
>
> More digits please.
> Fixes: d7fefcc8de91 ("mm/cma: add PF flag to force non cma alloc")
Will do.
> > Cc: <stable@...r.kernel.org>
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> > ---
> > include/linux/sched/mm.h | 4 ----
> > mm/page_alloc.c | 27 +++++++++++++++------------
> > 2 files changed, 15 insertions(+), 16 deletions(-)
> >
> > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> > index 44ad5b7..a73847a 100644
> > --- a/include/linux/sched/mm.h
> > +++ b/include/linux/sched/mm.h
> > @@ -191,10 +191,6 @@ static inline gfp_t current_gfp_context(gfp_t flags)
> > flags &= ~(__GFP_IO | __GFP_FS);
> > else if (pflags & PF_MEMALLOC_NOFS)
> > flags &= ~__GFP_FS;
>
> Above this hunk you should also remove PF_MEMALLOC_NOCMA from the test.
Will do.
> > -#ifdef CONFIG_CMA
> > - if (pflags & PF_MEMALLOC_NOCMA)
> > - flags &= ~__GFP_MOVABLE;
> > -#endif
> > }
> > return flags;
> > }
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 6416d08..cd53894 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2791,7 +2791,7 @@ __rmqueue(struct zone *zone, unsigned int order, int migratetype,
> > * allocating from CMA when over half of the zone's free memory
> > * is in the CMA area.
> > */
> > - if (migratetype == MIGRATE_MOVABLE &&
> > + if (alloc_flags & ALLOC_CMA &&
> > zone_page_state(zone, NR_FREE_CMA_PAGES) >
> > zone_page_state(zone, NR_FREE_PAGES) / 2) {
> > page = __rmqueue_cma_fallback(zone, order);
> > @@ -2802,7 +2802,7 @@ __rmqueue(struct zone *zone, unsigned int order, int migratetype,
> > retry:
> > page = __rmqueue_smallest(zone, order, migratetype);
> > if (unlikely(!page)) {
> > - if (migratetype == MIGRATE_MOVABLE)
> > + if (alloc_flags & ALLOC_CMA)
> > page = __rmqueue_cma_fallback(zone, order);
> >
> > if (!page && __rmqueue_fallback(zone, order, migratetype,
> > @@ -3502,11 +3502,9 @@ static inline long __zone_watermark_unusable_free(struct zone *z,
> > if (likely(!alloc_harder))
> > unusable_free += z->nr_reserved_highatomic;
> >
> > -#ifdef CONFIG_CMA
> > /* If allocation can't use CMA areas don't use free CMA pages */
> > - if (!(alloc_flags & ALLOC_CMA))
> > + if (IS_ENABLED(CONFIG_CMA) && !(alloc_flags & ALLOC_CMA))
> > unusable_free += zone_page_state(z, NR_FREE_CMA_PAGES);
> > -#endif
> >
> > return unusable_free;
> > }
> > @@ -3693,6 +3691,16 @@ alloc_flags_nofragment(struct zone *zone, gfp_t gfp_mask)
> > return alloc_flags;
> > }
> >
> > +static inline void current_alloc_flags(gfp_t gfp_mask,
> > + unsigned int *alloc_flags)
> > +{
> > + unsigned int pflags = READ_ONCE(current->flags);
> > +
> > + if (!(pflags & PF_MEMALLOC_NOCMA) &&
> > + gfp_migratetype(gfp_mask) == MIGRATE_MOVABLE)
> > + *alloc_flags |= ALLOC_CMA;
> > +}
>
> I don't like the modification through parameter, would just do what
> current_gfp_context() does and return the modified value.
> Also make it a no-op (including no READ_ONCE(current->flags)) if !CONFIG_CMA,
> please.
Okay.
> > /*
> > * get_page_from_freelist goes through the zonelist trying to allocate
> > * a page.
> > @@ -3706,6 +3714,8 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
> > struct pglist_data *last_pgdat_dirty_limit = NULL;
> > bool no_fallback;
> >
> > + current_alloc_flags(gfp_mask, &alloc_flags);
>
> I don't see why to move the test here? It will still be executed in the
> fastpath, if that's what you wanted to avoid.
I want to execute it on the fastpath, too. Reason that I moved it here
is that alloc_flags could be reset on slowpath. See the code where
__gfp_pfmemalloc_flags() is on. This is the only place that I can apply
this option to all the allocation paths at once.
Thanks.
> > +
> > retry:
> > /*
> > * Scan zonelist, looking for a zone with enough free.
> > @@ -4339,10 +4349,6 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
> > } else if (unlikely(rt_task(current)) && !in_interrupt())
> > alloc_flags |= ALLOC_HARDER;
> >
> > -#ifdef CONFIG_CMA
> > - if (gfp_migratetype(gfp_mask) == MIGRATE_MOVABLE)
> > - alloc_flags |= ALLOC_CMA;
> > -#endif
>
> I would just replace this here with:
> alloc_flags = current_alloc_flags(gfp_mask, alloc_flags);
>
> > return alloc_flags;
> > }
> >
> > @@ -4808,9 +4814,6 @@ static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order,
> > if (should_fail_alloc_page(gfp_mask, order))
> > return false;
> >
> > - if (IS_ENABLED(CONFIG_CMA) && ac->migratetype == MIGRATE_MOVABLE)
> > - *alloc_flags |= ALLOC_CMA;
>
> And same here... Ah, I see. current_alloc_flags() should probably take a
> migratetype parameter instead of gfp_mask then.
>
> > -
> > return true;
> > }
> >
> >
>
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