From: Jerome Marchand <jmarchan@redhat.com>
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>,
Dave Hansen <dave.hansen@intel.com>,
Hugh Dickins <hughd@google.com>, Mel Gorman <mgorman@suse.de>,
Rik van Riel <riel@redhat.com>, Vlastimil Babka <vbabka@suse.cz>,
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>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 06/19] mm: store mapcount for compound page separate
Date: Wed, 19 Nov 2014 14:15:24 +0100 [thread overview]
Message-ID: <546C97EC.10905@redhat.com> (raw)
In-Reply-To: <20141119130050.GA29884@node.dhcp.inet.fi>
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On 11/19/2014 02:00 PM, Kirill A. Shutemov wrote:
> On Wed, Nov 19, 2014 at 11:51:09AM +0100, Jerome Marchand wrote:
>> On 11/05/2014 03:49 PM, Kirill A. Shutemov wrote:
>>> We're going to allow mapping of individual 4k pages of THP compound and
>>> we need a cheap way to find out how many time the compound page is
>>> mapped with PMD -- compound_mapcount() does this.
>>>
>>> page_mapcount() counts both: PTE and PMD mappings of the page.
>>>
>>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>>> ---
>>> include/linux/mm.h | 17 +++++++++++++++--
>>> include/linux/rmap.h | 4 ++--
>>> mm/huge_memory.c | 23 ++++++++++++++---------
>>> mm/hugetlb.c | 4 ++--
>>> mm/memory.c | 2 +-
>>> mm/migrate.c | 2 +-
>>> mm/page_alloc.c | 13 ++++++++++---
>>> mm/rmap.c | 50 +++++++++++++++++++++++++++++++++++++++++++-------
>>> 8 files changed, 88 insertions(+), 27 deletions(-)
>>>
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index 1825c468f158..aef03acff228 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -435,6 +435,19 @@ static inline struct page *compound_head(struct page *page)
>>> return page;
>>> }
>>>
>>> +static inline atomic_t *compound_mapcount_ptr(struct page *page)
>>> +{
>>> + return (atomic_t *)&page[1].mapping;
>>> +}
>>
>> IIUC your patch overloads the unused mapping field of the first tail
>> page to store the PMD mapcount. That's a non obvious trick. Why not make
>> it more explicit by adding a new field (say compound_mapcount - and the
>> appropriate comment of course) to the union to which mapping already belong?
>
> I don't think we want to bloat struct page description: nobody outside of
> helpers should use it direcly. And it's exactly what we did to store
> compound page destructor and compound page order.
Yes, but hiding it might make people think this field is unused when
it's not. If it has been done that way for a while, maybe it's not as
much trouble as I think it is, but could you at least add a comment in
the helper.
>
>> The patch description would benefit from more explanation too.
>
> Agreed.
>
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next prev parent reply other threads:[~2014-11-19 13:16 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-05 14:49 [PATCHv2 RFC 00/19] THP refcounting redesign Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 01/19] mm, thp: drop FOLL_SPLIT Kirill A. Shutemov
2014-11-25 3:01 ` Naoya Horiguchi
2014-11-25 14:04 ` Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 02/19] thp: cluster split_huge_page* code together Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 03/19] mm: change PageAnon() to work on tail pages Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 04/19] mm: avoid PG_locked " Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 05/19] rmap: add argument to charge compound page Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 06/19] mm: store mapcount for compound page separate Kirill A. Shutemov
2014-11-18 8:43 ` Naoya Horiguchi
2014-11-18 9:58 ` Kirill A. Shutemov
2014-11-18 23:41 ` Naoya Horiguchi
2014-11-19 0:54 ` Kirill A. Shutemov
2014-11-21 6:41 ` Aneesh Kumar K.V
2014-11-21 11:47 ` Kirill A. Shutemov
2014-11-19 10:51 ` Jerome Marchand
2014-11-19 13:00 ` Kirill A. Shutemov
2014-11-19 13:15 ` Jerome Marchand [this message]
2014-11-20 20:06 ` Christoph Lameter
2014-11-21 12:01 ` Kirill A. Shutemov
2014-11-21 6:12 ` Aneesh Kumar K.V
2014-11-21 12:02 ` Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 07/19] mm, thp: adjust conditions when we can reuse the page on WP fault Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 08/19] mm: prepare migration code for new THP refcounting Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 09/19] thp: rename split_huge_page_pmd() to split_huge_pmd() Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 10/19] thp: PMD splitting without splitting compound page Kirill A. Shutemov
2014-11-19 6:57 ` Naoya Horiguchi
2014-11-19 13:02 ` Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 11/19] mm, vmstats: new THP splitting event Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 12/19] thp: implement new split_huge_page() Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 13/19] mm, thp: remove infrastructure for handling splitting PMDs Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 14/19] x86, thp: remove " Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 15/19] futex, thp: remove special case for THP in get_futex_key Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 16/19] thp: update documentation Kirill A. Shutemov
2014-11-19 8:07 ` Naoya Horiguchi
2014-11-19 13:11 ` Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 17/19] mlock, thp: HACK: split all pages in VM_LOCKED vma Kirill A. Shutemov
2014-11-19 9:02 ` Naoya Horiguchi
2014-11-19 13:08 ` Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 18/19] tho, mm: use migration entries to freeze page counts on split Kirill A. Shutemov
2014-11-05 14:49 ` [PATCH 19/19] mm, thp: remove compound_lock Kirill A. Shutemov
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