Messages in this thread | | | Date | Mon, 28 Sep 2020 16:52:15 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v2 for v5.9] mm/page_alloc: handle a missing case for memalloc_nocma_{save/restore} APIs |
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On Mon, 28 Sep 2020 17:50:46 +0900 js1304@gmail.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com> > > memalloc_nocma_{save/restore} APIs can be used to skip page allocation > on CMA area, but, there is a missing case and the page on CMA area could > be allocated even if APIs are used. This patch handles this case to fix > the potential issue. > > Missing case is an allocation from the pcplist. MIGRATE_MOVABLE pcplist > could have the pages on CMA area so we need to skip it if ALLOC_CMA isn't > specified.
Changelog doesn't describe the end-user visible effects of the bug. Please send this description?
> --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3367,9 +3367,16 @@ struct page *rmqueue(struct zone *preferred_zone, > struct page *page; > > if (likely(order == 0)) { > - page = rmqueue_pcplist(preferred_zone, zone, gfp_flags, > + /* > + * MIGRATE_MOVABLE pcplist could have the pages on CMA area and > + * we need to skip it when CMA area isn't allowed. > + */ > + if (!IS_ENABLED(CONFIG_CMA) || alloc_flags & ALLOC_CMA || > + migratetype != MIGRATE_MOVABLE) { > + page = rmqueue_pcplist(preferred_zone, zone, gfp_flags, > migratetype, alloc_flags); > - goto out; > + goto out; > + } > } > > /*
We still really really don't want to be adding overhead to the page allocation hotpath for a really really obscure feature from a single callsite.
Do we have an understanding of how many people's kernels are enabling CONFIG_CMA?
I previously suggested retrying the allocation in __gup_longterm_locked() but you said "it cannot ensure that we eventually get the non-CMA page". Please explain why?
What about manually emptying the pcplists beforehand?
Or byassing the pcplists for this caller and calling __rmqueue() directly?
> @@ -3381,7 +3388,7 @@ struct page *rmqueue(struct zone *preferred_zone, > > do { > page = NULL; > - if (alloc_flags & ALLOC_HARDER) { > + if (order > 0 && alloc_flags & ALLOC_HARDER) { > page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC); > if (page) > trace_mm_page_alloc_zone_locked(page, order, migratetype);
What does this hunk do?
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