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SubjectRe: [PATCH 1/4] mm/page_alloc: fix non cma alloc context
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On 7/16/20 9:27 AM, Joonsoo Kim wrote:
> 2020년 7월 15일 (수) 오후 5:24, Vlastimil Babka <vbabka@suse.cz>님이 작성:
>> > /*
>> > * 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.

But get_page_from_freelist() might be called multiple times in the slowpath, and
also anyone looking for gfp and alloc flags setup will likely not examine this
function. I don't see a problem in having it in two places that already deal
with alloc_flags setup, as it is now.

> 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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