From: Vlastimil Babka <vbabka@suse.cz>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Hugh Dickins <hughd@google.com>,
Dave Hansen <dave.hansen@intel.com>, Mel Gorman <mgorman@suse.de>,
Rik van Riel <riel@redhat.com>, Christoph Lameter <cl@gentwo.org>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Steve Capper <steve.capper@linaro.org>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.cz>,
Jerome Marchand <jmarchan@redhat.com>,
Sasha Levin <sasha.levin@oracle.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv6 36/36] thp: update documentation
Date: Mon, 22 Jun 2015 18:07:00 +0200 [thread overview]
Message-ID: <558832A4.6060609@suse.cz> (raw)
In-Reply-To: <20150622131827.GF7934@node.dhcp.inet.fi>
On 06/22/2015 03:18 PM, Kirill A. Shutemov wrote:
> On Thu, Jun 11, 2015 at 02:30:15PM +0200, Vlastimil Babka wrote:
>> On 06/03/2015 07:06 PM, Kirill A. Shutemov wrote:
>>> The patch updates Documentation/vm/transhuge.txt to reflect changes in
>>> THP design.
>>
>> One thing I'm missing is info about the deferred splitting.
>
> Okay, I'll add this.
Thanks.
>>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>>> ---
>>> Documentation/vm/transhuge.txt | 124 +++++++++++++++++++++++------------------
>>> 1 file changed, 69 insertions(+), 55 deletions(-)
>>>
>>> diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
>>> index 6b31cfbe2a9a..2352b12cae93 100644
>>> --- a/Documentation/vm/transhuge.txt
>>> +++ b/Documentation/vm/transhuge.txt
>>> @@ -35,10 +35,10 @@ miss is going to run faster.
>>>
>>> == Design ==
>>>
>>> -- "graceful fallback": mm components which don't have transparent
>>> - hugepage knowledge fall back to breaking a transparent hugepage and
>>> - working on the regular pages and their respective regular pmd/pte
>>> - mappings
>>> +- "graceful fallback": mm components which don't have transparent hugepage
>>> + knowledge fall back to breaking huge pmd mapping into table of ptes and,
>>> + if nesessary, split a transparent hugepage. Therefore these components
>>
>> necessary
>>> +
>>> +split_huge_page uses migration entries to stabilize page->_count and
>>> +page->_mapcount.
>>
>> Hm, what if there's some physical memory scanner taking page->_count pins? I
>> think compaction shouldn't be an issue, but maybe some others?
>
> The only legitimate way scanner can get reference to a page is
> get_page_unless_zero(), right?
I think so.
> All tail pages has zero ->_count until atomic_add() in
> __split_huge_page_tail() -- get_page_unless_zero() will fail.
> After the atomic_add() we don't care about ->_count value.
> We already known how many references with should uncharge from
> head page.
>
> For head page get_page_unless_zero() will succeed and we don't
> mind. It's clear where reference should go after split: it will
> stay on head page.
I guess that works, but it's rather non-obvious thus worth documenting
somewhere.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
Please read the FAQ at http://www.tux.org/lkml/
WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Hugh Dickins <hughd@google.com>,
Dave Hansen <dave.hansen@intel.com>, Mel Gorman <mgorman@suse.de>,
Rik van Riel <riel@redhat.com>, Christoph Lameter <cl@gentwo.org>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Steve Capper <steve.capper@linaro.org>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.cz>,
Jerome Marchand <jmarchan@redhat.com>,
Sasha Levin <sasha.levin@oracle.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv6 36/36] thp: update documentation
Date: Mon, 22 Jun 2015 18:07:00 +0200 [thread overview]
Message-ID: <558832A4.6060609@suse.cz> (raw)
In-Reply-To: <20150622131827.GF7934@node.dhcp.inet.fi>
On 06/22/2015 03:18 PM, Kirill A. Shutemov wrote:
> On Thu, Jun 11, 2015 at 02:30:15PM +0200, Vlastimil Babka wrote:
>> On 06/03/2015 07:06 PM, Kirill A. Shutemov wrote:
>>> The patch updates Documentation/vm/transhuge.txt to reflect changes in
>>> THP design.
>>
>> One thing I'm missing is info about the deferred splitting.
>
> Okay, I'll add this.
Thanks.
>>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>>> ---
>>> Documentation/vm/transhuge.txt | 124 +++++++++++++++++++++++------------------
>>> 1 file changed, 69 insertions(+), 55 deletions(-)
>>>
>>> diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
>>> index 6b31cfbe2a9a..2352b12cae93 100644
>>> --- a/Documentation/vm/transhuge.txt
>>> +++ b/Documentation/vm/transhuge.txt
>>> @@ -35,10 +35,10 @@ miss is going to run faster.
>>>
>>> == Design ==
>>>
>>> -- "graceful fallback": mm components which don't have transparent
>>> - hugepage knowledge fall back to breaking a transparent hugepage and
>>> - working on the regular pages and their respective regular pmd/pte
>>> - mappings
>>> +- "graceful fallback": mm components which don't have transparent hugepage
>>> + knowledge fall back to breaking huge pmd mapping into table of ptes and,
>>> + if nesessary, split a transparent hugepage. Therefore these components
>>
>> necessary
>>> +
>>> +split_huge_page uses migration entries to stabilize page->_count and
>>> +page->_mapcount.
>>
>> Hm, what if there's some physical memory scanner taking page->_count pins? I
>> think compaction shouldn't be an issue, but maybe some others?
>
> The only legitimate way scanner can get reference to a page is
> get_page_unless_zero(), right?
I think so.
> All tail pages has zero ->_count until atomic_add() in
> __split_huge_page_tail() -- get_page_unless_zero() will fail.
> After the atomic_add() we don't care about ->_count value.
> We already known how many references with should uncharge from
> head page.
>
> For head page get_page_unless_zero() will succeed and we don't
> mind. It's clear where reference should go after split: it will
> stay on head page.
I guess that works, but it's rather non-obvious thus worth documenting
somewhere.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2015-06-22 16:07 UTC|newest]
Thread overview: 114+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-03 17:05 [PATCHv6 00/36] THP refcounting redesign Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 01/36] mm, proc: adjust PSS calculation Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-09 12:29 ` Vlastimil Babka
2015-06-09 12:29 ` Vlastimil Babka
2015-06-22 10:02 ` Kirill A. Shutemov
2015-06-22 10:02 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 02/36] rmap: add argument to charge compound page Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 03/36] memcg: adjust to support new THP refcounting Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 04/36] mm, thp: adjust conditions when we can reuse the page on WP fault Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 05/36] mm: adjust FOLL_SPLIT for new refcounting Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 06/36] mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 07/36] thp, mlock: do not allow huge pages in mlocked area Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 08/36] khugepaged: ignore pmd tables with THP mapped with ptes Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 09/36] thp: rename split_huge_page_pmd() to split_huge_pmd() Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 10/36] mm, vmstats: new THP splitting event Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 11/36] mm: temporally mark THP broken Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 12/36] thp: drop all split_huge_page()-related code Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 13/36] mm: drop tail page refcounting Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-09 13:59 ` Vlastimil Babka
2015-06-09 13:59 ` Vlastimil Babka
2015-06-03 17:05 ` [PATCHv6 14/36] futex, thp: remove special case for THP in get_futex_key Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 15/36] ksm: prepare to new THP semantics Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 16/36] mm, thp: remove compound_lock Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 17/36] arm64, thp: remove infrastructure for handling splitting PMDs Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 18/36] arm, " Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 19/36] mips, " Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 20/36] powerpc, " Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 21/36] s390, " Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 22/36] sparc, " Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 23/36] tile, " Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 24/36] x86, " Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 25/36] mm, " Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 26/36] mm: rework mapcount accounting to enable 4k mapping of THPs Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-10 13:47 ` Vlastimil Babka
2015-06-10 13:47 ` Vlastimil Babka
2015-06-22 10:22 ` Kirill A. Shutemov
2015-06-22 10:22 ` Kirill A. Shutemov
2015-06-03 17:05 ` [PATCHv6 27/36] mm: differentiate page_mapped() from page_mapcount() for compound pages Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-09 10:58 ` Kirill A. Shutemov
2015-06-09 10:58 ` Kirill A. Shutemov
2015-06-10 14:34 ` Vlastimil Babka
2015-06-10 14:34 ` Vlastimil Babka
2015-06-03 17:05 ` [PATCHv6 28/36] mm, numa: skip PTE-mapped THP on numa fault Kirill A. Shutemov
2015-06-03 17:05 ` Kirill A. Shutemov
2015-06-03 17:06 ` [PATCHv6 29/36] thp: implement split_huge_pmd() Kirill A. Shutemov
2015-06-03 17:06 ` Kirill A. Shutemov
2015-06-11 9:49 ` Vlastimil Babka
2015-06-11 9:49 ` Vlastimil Babka
2015-06-22 11:14 ` Kirill A. Shutemov
2015-06-22 11:14 ` Kirill A. Shutemov
2015-06-22 16:01 ` Vlastimil Babka
2015-06-22 16:01 ` Vlastimil Babka
2015-06-03 17:06 ` [PATCHv6 30/36] thp: add option to setup migration entiries during PMD split Kirill A. Shutemov
2015-06-03 17:06 ` Kirill A. Shutemov
2015-06-03 17:06 ` [PATCHv6 31/36] thp, mm: split_huge_page(): caller need to lock page Kirill A. Shutemov
2015-06-03 17:06 ` Kirill A. Shutemov
2015-06-03 17:06 ` [PATCHv6 32/36] thp: reintroduce split_huge_page() Kirill A. Shutemov
2015-06-03 17:06 ` Kirill A. Shutemov
2015-06-10 15:44 ` Vlastimil Babka
2015-06-10 15:44 ` Vlastimil Babka
2015-06-22 11:28 ` Kirill A. Shutemov
2015-06-22 11:28 ` Kirill A. Shutemov
2015-06-03 17:06 ` [PATCHv6 33/36] migrate_pages: try to split pages on qeueuing Kirill A. Shutemov
2015-06-03 17:06 ` Kirill A. Shutemov
2015-06-11 9:27 ` Vlastimil Babka
2015-06-11 9:27 ` Vlastimil Babka
2015-06-22 11:35 ` Kirill A. Shutemov
2015-06-22 11:35 ` Kirill A. Shutemov
2015-06-03 17:06 ` [PATCHv6 34/36] thp: introduce deferred_split_huge_page() Kirill A. Shutemov
2015-06-03 17:06 ` Kirill A. Shutemov
2015-06-03 17:06 ` [PATCHv6 35/36] mm: re-enable THP Kirill A. Shutemov
2015-06-03 17:06 ` Kirill A. Shutemov
2015-06-03 17:06 ` [PATCHv6 36/36] thp: update documentation Kirill A. Shutemov
2015-06-03 17:06 ` Kirill A. Shutemov
2015-06-11 12:30 ` Vlastimil Babka
2015-06-11 12:30 ` Vlastimil Babka
2015-06-22 13:18 ` Kirill A. Shutemov
2015-06-22 13:18 ` Kirill A. Shutemov
2015-06-22 16:07 ` Vlastimil Babka [this message]
2015-06-22 16:07 ` Vlastimil Babka
2015-06-16 13:17 ` [PATCHv6 00/36] THP refcounting redesign Jerome Marchand
2015-06-22 13:21 ` Kirill A. Shutemov
2015-06-22 13:21 ` Kirill A. Shutemov
2015-06-22 13:32 ` Jerome Marchand
2015-06-22 13:39 ` Kirill A. Shutemov
2015-06-22 13:39 ` Kirill A. Shutemov
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=558832A4.6060609@suse.cz \
--to=vbabka@suse.cz \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=aneesh.kumar@linux.vnet.ibm.com \
--cc=cl@gentwo.org \
--cc=dave.hansen@intel.com \
--cc=hannes@cmpxchg.org \
--cc=hughd@google.com \
--cc=jmarchan@redhat.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=kirill@shutemov.name \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@suse.de \
--cc=mhocko@suse.cz \
--cc=n-horiguchi@ah.jp.nec.com \
--cc=riel@redhat.com \
--cc=sasha.levin@oracle.com \
--cc=steve.capper@linaro.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.