From: Mike Kravetz <mike.kravetz@oracle.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
linux-mm@kvack.org, akpm@linux-foundation.org
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH V3 1/3] arm64/mm: Drop __HAVE_ARCH_HUGE_PTEP_GET
Date: Mon, 11 May 2020 11:49:52 -0700 [thread overview]
Message-ID: <7642f615-23ff-56c7-25da-f84c409449b5@oracle.com> (raw)
In-Reply-To: <19ffbe33-3a42-6d90-6c48-19645a898383@arm.com>
On 5/10/20 9:02 PM, Anshuman Khandual wrote:
> On 05/09/2020 03:39 AM, Mike Kravetz wrote:
>> On 5/7/20 8:07 PM, Anshuman Khandual wrote:
>> I know you made this change in response to Will's comment. And, since
>> changes were made to consistently use READ_ONCE in arm64 code, it makes
>> sense for that architecture.
>>
>> However, with this change to generic code, you introduce READ_ONCE to
>> other architectures where it was not used before. Could this possibly
>> introduce inconsistencies in their use of READ_ONCE? To be honest, I
>> am not very good at identifying any possible issues this could cause.
>> However, it does seem possible.
>
> Could you please give some more details. Is there any particular problem
> which might be caused by this new READ_ONCE() here, that you you are
> concerned about. READ_ONCE() is already getting used in multiple places
> in core MM which can not be configured out (like mm/gup.c). It is getting
> used in core HugeTLB (mm/hugetlb.c) as well. AFAICS, there is no standard
> for using READ_ONCE() while walking page tables entries. We have examples
> in core MM for both ways.
>
>>
>> Will was nervous about dropping this from arm64. I'm just a little nervous
>> about adding it to other architectures.
>>
> AFAICS, __HAVE_ARCH_HUGE_PTEP_GET should be used on a platform only when
> a HugeTLB entry could not constructed by dereferencing a page table entry
> as in the case with ARM (32 bit). Using READ_ONCE() while dereferencing is
> really not a special case that will need __HAVE_ARCH_HUGE_PTEP_GET. Moving
> READ_ONCE() into generic definition solves the problem while also taking
> care of a known problem on arm64. IMHO, it seems like the right thing to
> do unless there is another problem that pops up some where else because of
> READ_ONCE().
I have no specific concerns or objection. After thinking about it some more,
I do not see how adding the READ_ONCE could cause any issues.
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
--
Mike Kravetz
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-05-11 18:50 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-08 3:07 [PATCH V3 0/3] mm/hugetlb: Add some new generic fallbacks Anshuman Khandual
2020-05-08 3:07 ` [PATCH V3 1/3] arm64/mm: Drop __HAVE_ARCH_HUGE_PTEP_GET Anshuman Khandual
2020-05-08 22:09 ` Mike Kravetz
2020-05-11 4:02 ` Anshuman Khandual
2020-05-11 18:49 ` Mike Kravetz [this message]
2020-05-08 3:07 ` [PATCH V3 2/3] mm/hugetlb: Define a generic fallback for is_hugepage_only_range() Anshuman Khandual
2020-05-08 22:22 ` Mike Kravetz
2020-05-11 3:14 ` Anshuman Khandual
2020-05-11 18:52 ` Mike Kravetz
2020-05-08 3:07 ` [PATCH V3 3/3] mm/hugetlb: Define a generic fallback for arch_clear_hugepage_flags() Anshuman Khandual
2020-05-11 20:22 ` Mike Kravetz
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=7642f615-23ff-56c7-25da-f84c409449b5@oracle.com \
--to=mike.kravetz@oracle.com \
--cc=akpm@linux-foundation.org \
--cc=anshuman.khandual@arm.com \
--cc=catalin.marinas@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=will@kernel.org \
/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).