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Date: Fri, 17 Feb 2017 17:09:57 +0100 From: Vlastimil Babka <vbabka@...e.cz> To: Johannes Weiner <hannes@...xchg.org> Cc: linux-mm@...ck.org, Joonsoo Kim <iamjoonsoo.kim@....com>, David Rientjes <rientjes@...gle.com>, Mel Gorman <mgorman@...hsingularity.net>, linux-kernel@...r.kernel.org, kernel-team@...com Subject: Re: [PATCH v2 04/10] mm, page_alloc: count movable pages when stealing from pageblock On 02/14/2017 07:10 PM, Johannes Weiner wrote: > > That makes sense to me. I have just one nit about the patch: > >> @@ -1981,10 +1994,29 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page, >> return; >> } >> >> - pages = move_freepages_block(zone, page, start_type); >> + free_pages = move_freepages_block(zone, page, start_type, >> + &good_pages); >> + /* >> + * good_pages is now the number of movable pages, but if we >> + * want UNMOVABLE or RECLAIMABLE allocation, it's more tricky >> + */ >> + if (start_type != MIGRATE_MOVABLE) { >> + /* >> + * If we are falling back to MIGRATE_MOVABLE pageblock, >> + * treat all non-movable pages as good. If it's UNMOVABLE >> + * falling back to RECLAIMABLE or vice versa, be conservative >> + * as we can't distinguish the exact migratetype. >> + */ >> + old_block_type = get_pageblock_migratetype(page); >> + if (old_block_type == MIGRATE_MOVABLE) >> + good_pages = pageblock_nr_pages >> + - free_pages - good_pages; > > This line had me scratch my head for a while, and I think it's mostly > because of the variable naming and the way the comments are phrased. > > Could you use a variable called movable_pages to pass to and be filled > in by move_freepages_block? > > And instead of good_pages something like starttype_pages or > alike_pages or st_pages or mt_pages or something, to indicate the > number of pages that are comparable to the allocation's migratetype? > >> - /* Claim the whole block if over half of it is free */ >> - if (pages >= (1 << (pageblock_order-1)) || >> + /* Claim the whole block if over half of it is free or good type */ >> + if (free_pages + good_pages >= (1 << (pageblock_order-1)) || >> page_group_by_mobility_disabled) >> set_pageblock_migratetype(page, start_type); > > This would then read > > if (free_pages + alike_pages ...) > > which I think would be more descriptive. > > The comment leading the entire section following move_freepages_block > could then say something like "If a sufficient number of pages in the > block are either free or of comparable migratability as our > allocation, claim the whole block." Followed by the caveats of how we > determine this migratibility. > > Or maybe even the function. The comment above the function seems out > of date after this patch. I'll incorporate this for the next posting, thanks for the feedback!
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