linux-kernel - Re: [PATCH V2 2/5] mm/hugetlb: Distinguish between migratability and movability

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Message-ID: <e7a3d5d8-dc65-72fc-5764-010af02d1517@arm.com>
Date:   Fri, 19 Oct 2018 08:02:26 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "suzuki.poulose@....com" <suzuki.poulose@....com>,
        "punit.agrawal@....com" <punit.agrawal@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "Steven.Price@....com" <Steven.Price@....com>,
        "steve.capper@....com" <steve.capper@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>
Subject: Re: [PATCH V2 2/5] mm/hugetlb: Distinguish between migratability and
 movability



On 10/19/2018 07:29 AM, Naoya Horiguchi wrote:
> On Fri, Oct 12, 2018 at 09:29:56AM +0530, Anshuman Khandual wrote:
>> During huge page allocation it's migratability is checked to determine if
>> it should be placed under movable zones with GFP_HIGHUSER_MOVABLE. But the
>> movability aspect of the huge page could depend on other factors than just
>> migratability. Movability in itself is a distinct property which should not
>> be tied with migratability alone.
>>
>> This differentiates these two and implements an enhanced movability check
>> which also considers huge page size to determine if it is feasible to be
>> placed under a movable zone. At present it just checks for gigantic pages
>> but going forward it can incorporate other enhanced checks.
> 
> (nitpicking...)
> The following code just checks hugepage_migration_supported(), so maybe
> s/Movability/Migratability/ is expected in the comment?
> 
>   static int unmap_and_move_huge_page(...)
>   {
>           ...
>           /*
>            * Movability of hugepages depends on architectures and hugepage size.
>            * This check is necessary because some callers of hugepage migration
>            * like soft offline and memory hotremove don't walk through page
>            * tables or check whether the hugepage is pmd-based or not before
>            * kicking migration.
>            */
>           if (!hugepage_migration_supported(page_hstate(hpage))) {
> 
Sure, will update this patch only unless other changes are suggested.