From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
Zi Yan <zi.yan@cs.rutgers.edu>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kirill.shutemov@linux.intel.com, akpm@linux-foundation.org,
mhocko@suse.com, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [PATCH] mm/thp: Correctly differentiate between mapped THP and PMD migration entry
Date: Tue, 6 Nov 2018 15:21:46 +0530 [thread overview]
Message-ID: <9370f2b9-0fcd-6bbb-fa29-568bbd9aba59@arm.com> (raw)
In-Reply-To: <20181106003509.GA27283@brain-police>
On 11/06/2018 06:05 AM, Will Deacon wrote:
> On Fri, Nov 02, 2018 at 11:45:00AM +0530, Anshuman Khandual wrote:
>> On 10/17/2018 07:39 AM, Andrea Arcangeli wrote:
>>> What we need to do during split is an invalidate of the huge TLB.
>>> There's no pmd_trans_splitting anymore, so we only clear the present
>>> bit in the PTE despite pmd_present still returns true (just like
>>> PROT_NONE, nothing new in this respect). pmd_present never meant the
>>
>> On arm64, the problem is that pmd_present() is tied with pte_present() which
>> checks for PTE_VALID (also PTE_PROT_NONE) but which gets cleared during PTE
>> invalidation. pmd_present() returns false just after the first step of PMD
>> splitting. So pmd_present() needs to be decoupled from PTE_VALID which is
>> same as PMD_SECT_VALID and instead should depend upon a pte bit which sticks
>> around like PAGE_PSE as in case of x86. I am working towards a solution.
>
> Could we not just go via a PROT_NONE mapping during the split, instead of
> having to allocate a new software bit to treat these invalid ptes as
> present?
The problem might occur during page fault (i.e __handle_mm_fault). As discussed
previously on this thread any potential PTE sticky bit would be used for both
pmd_trans_huge() and pmd_present() wrappers to maintain existing semantics. At
present, PMD state analysis during page fault has conditional block like this.
if (pmd_trans_huge(orig_pmd) || pmd_devmap(orig_pmd)) {
if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
return do_huge_pmd_numa_page(&vmf, orig_pmd);
Using PROT_NONE for pmd_trans_huge() might force PMD page fault to go through
NUMA fault handling all the time as both pmd_trans_huge() and pmd_protnone()
will return true in that situation.
prev parent reply other threads:[~2018-11-06 9:51 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
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 [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=9370f2b9-0fcd-6bbb-fa29-568bbd9aba59@arm.com \
--to=anshuman.khandual@arm.com \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.com \
--cc=n-horiguchi@ah.jp.nec.com \
--cc=will.deacon@arm.com \
--cc=zi.yan@cs.rutgers.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).