Re: [PATCH v5 05/14] mm, compaction: move pageblock checks up from isolate_migratepages_range()

[David Rientjes]

On Wed, 30 Jul 2014, Kirill A. Shutemov wrote:

> > Hmm, I'm confused at how that could be true, could you explain what 
> > memory other than thp can return true for PageTransHuge()?
> 
> PageTransHuge() will be true for any head of compound page if THP is
> enabled compile time: hugetlbfs, slab, whatever.
> 

I was meaning in the context of the patch :)  Since PageLRU is set, that 
discounts slab so we're left with thp or hugetlbfs.  Logically, both 
should have sizes that are >= the size of the pageblock itself so I'm not 
sure why we don't unconditionally align up to pageblock_nr_pages here.  Is 
there a legitimiate configuration where a pageblock will span multiple 
pages of HPAGE_PMD_ORDER?
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