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Date: Thu, 01 Aug 2013 11:29:39 +0530 From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> To: Naoya Horiguchi <n-horiguchi@...jp.nec.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Andi Kleen <andi@...stfloor.org>, Hillf Danton <dhillf@...il.com>, Michal Hocko <mhocko@...e.cz>, Rik van Riel <riel@...hat.com>, Wanpeng Li <liwanp@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org, Naoya Horiguchi <nao.horiguchi@...il.com> Subject: Re: [PATCH 8/8] prepare to remove /proc/sys/vm/hugepages_treat_as_movable Naoya Horiguchi <n-horiguchi@...jp.nec.com> writes: > On Wed, Jul 31, 2013 at 12:02:30AM +0530, Aneesh Kumar K.V wrote: >> Naoya Horiguchi <n-horiguchi@...jp.nec.com> writes: >> >> > Now hugepages are definitely movable. So allocating hugepages from >> > ZONE_MOVABLE is natural and we have no reason to keep this parameter. >> > In order to allow userspace to prepare for the removal, let's leave >> > this sysctl handler as noop for a while. >> >> I guess you still need to handle architectures for which pmd_huge is >> >> int pmd_huge(pmd_t pmd) >> { >> return 0; >> } >> >> embedded powerpc is one. They don't store pte information at the PMD >> level. Instead pmd contains a pointer to hugepage directory which >> contain huge pte. > > It seems that this comment is for the whole series, not just for this > patch, right? > > Some users of hugepage migration (mbind, move_pages, migrate_pages) > walk over page tables to collect hugepages to be migrated, where > hugepages are just ignored in such architectures due to pmd_huge. > So no problem for these users. > > But the other users (softoffline, memory hotremove) choose hugepages > to be migrated based on pfn, where they don't check pmd_huge. > As you wrote, this can be problematic for such architectures. > So I think of adding pmd_huge() check somewhere (in unmap_and_move_huge_page > for example) to make it fail for such architectures. Considering that we have architectures that won't support migrating explicit hugepages with this patch series, is it ok to use GFP_HIGHUSER_MOVABLE for hugepage allocation ? -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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