From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
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>,
Steve Capper <steve.capper@linaro.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.cz>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm\@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH 06/19] mm: store mapcount for compound page separate
Date: Fri, 21 Nov 2014 12:11:34 +0530 [thread overview]
Message-ID: <87egsx6oo1.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <20141118095811.GA21774@node.dhcp.inet.fi>
"Kirill A. Shutemov" <kirill@shutemov.name> writes:
> On Tue, Nov 18, 2014 at 08:43:00AM +0000, Naoya Horiguchi wrote:
>> > @@ -1837,6 +1839,9 @@ static void __split_huge_page_refcount(struct page *page,
>> > atomic_sub(tail_count, &page->_count);
>> > BUG_ON(atomic_read(&page->_count) <= 0);
>> >
>> > + page->_mapcount = *compound_mapcount_ptr(page);
>>
>> Is atomic_set() necessary?
>
> Do you mean
> atomic_set(&page->_mapcount, atomic_read(compound_mapcount_ptr(page)));
> ?
>
> I don't see why we would need this. Simple assignment should work just
> fine. Or we have archs which will break?
Are you looking at architecture related atomic_set issues, or the fact
that we cannot have parallel _mapcount update and hence the above
assignment should be ok ? If the former, current thp code
use atomic_add instead of even using atomic_set when
updatinge page_tail->_count.
* from under us on the tail_page. If we used
* atomic_set() below instead of atomic_add(), we
* would then run atomic_set() concurrently with
* get_page_unless_zero(), and atomic_set() is
* implemented in C not using locked ops. spin_unlock
* on x86 sometime uses locked ops because of PPro
* errata 66, 92, so unless somebody can guarantee
* atomic_set() here would be safe on all archs (and
* not only on x86), it's safer to use atomic_add().
*/
atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
&page_tail->_count);
-aneesh
next prev parent reply other threads:[~2014-11-21 6:42 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 [this message]
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
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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