From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kirill.shutemov@linux.intel.com, akpm@linux-foundation.org,
mhocko@suse.com, zi.yan@cs.rutgers.edu, will.deacon@arm.com
Subject: Re: [PATCH] mm/thp: Correctly differentiate between mapped THP and PMD migration entry
Date: Tue, 9 Oct 2018 16:04:21 +0300 [thread overview]
Message-ID: <20181009130421.bmus632ocurn275u@kshutemo-mobl1> (raw)
In-Reply-To: <1539057538-27446-1-git-send-email-anshuman.khandual@arm.com>
On Tue, Oct 09, 2018 at 09:28:58AM +0530, Anshuman Khandual wrote:
> A normal mapped THP page at PMD level should be correctly differentiated
> from a PMD migration entry while walking the page table. A mapped THP would
> additionally check positive for pmd_present() along with pmd_trans_huge()
> as compared to a PMD migration entry. This just adds a new conditional test
> differentiating the two while walking the page table.
>
> Fixes: 616b8371539a6 ("mm: thp: enable thp migration in generic path")
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> On X86, pmd_trans_huge() and is_pmd_migration_entry() are always mutually
> exclusive which makes the current conditional block work for both mapped
> and migration entries. This is not same with arm64 where pmd_trans_huge()
> returns positive for both mapped and migration entries. Could some one
> please explain why pmd_trans_huge() has to return false for migration
> entries which just install swap bits and its still a PMD ?
I guess it's just a design choice. Any reason why arm64 cannot do the
same?
> Nonetheless pmd_present() seems to be a better check to distinguish
> between mapped and (non-mapped non-present) migration entries without
> any ambiguity.
Can we instead reverse order of check:
if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
pvmw->ptl = pmd_lock(mm, pvmw->pmd);
if (!pmd_present(*pvmw->pmd)) {
...
} else if (likely(pmd_trans_huge(*pvmw->pmd))) {
...
} else {
...
}
...
This should cover both imeplementations of pmd_trans_huge().
--
Kirill A. Shutemov
next prev parent reply other threads:[~2018-10-09 13:04 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-09 3:58 [PATCH] mm/thp: Correctly differentiate between mapped THP and PMD migration entry Anshuman Khandual
2018-10-09 13:04 ` Kirill A. Shutemov [this message]
2018-10-09 13:18 ` Will Deacon
2018-10-12 8:02 ` Anshuman Khandual
2018-10-15 8:32 ` Aneesh Kumar K.V
2018-10-16 13:16 ` Anshuman Khandual
2018-10-09 13:42 ` Anshuman Khandual
2018-10-09 13:58 ` Zi Yan
2018-10-10 4:05 ` Anshuman Khandual
2018-10-10 12:43 ` Zi Yan
2018-10-12 8:00 ` Anshuman Khandual
2018-10-15 0:53 ` Zi Yan
2018-10-15 4:06 ` Anshuman Khandual
2018-10-16 14:31 ` Zi Yan
2018-10-18 2:17 ` Naoya Horiguchi
2018-11-02 5:22 ` Anshuman Khandual
2018-10-25 8:10 ` Anshuman Khandual
2018-10-25 18:45 ` Zi Yan
2018-10-26 1:39 ` Anshuman Khandual
2018-10-17 2:09 ` Andrea Arcangeli
2018-10-22 14:00 ` Zi Yan
2018-11-02 6:15 ` Anshuman Khandual
2018-11-06 0:35 ` Will Deacon
2018-11-06 9:51 ` Anshuman Khandual
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