From: "Kirill A. Shutemov" <kirill@shutemov.name> To: Vlastimil Babka <vbabka@suse.cz> 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 29/36] thp: implement split_huge_pmd() Date: Mon, 22 Jun 2015 14:14:34 +0300 [thread overview] Message-ID: <20150622111434.GC7934@node.dhcp.inet.fi> (raw) In-Reply-To: <557959BC.5000303@suse.cz> On Thu, Jun 11, 2015 at 11:49:48AM +0200, Vlastimil Babka wrote: > On 06/03/2015 07:06 PM, Kirill A. Shutemov wrote: > >Original split_huge_page() combined two operations: splitting PMDs into > >tables of PTEs and splitting underlying compound page. This patch > >implements split_huge_pmd() which split given PMD without splitting > >other PMDs this page mapped with or underlying compound page. > > > >Without tail page refcounting, implementation of split_huge_pmd() is > >pretty straight-forward. > > > >Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > >Tested-by: Sasha Levin <sasha.levin@oracle.com> > > [...] > > >+ > >+ if (atomic_add_negative(-1, compound_mapcount_ptr(page))) { > >+ /* Last compound_mapcount is gone. */ > >+ __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES); > >+ if (PageDoubleMap(page)) { > >+ /* No need in mapcount reference anymore */ > >+ ClearPageDoubleMap(page); > >+ for (i = 0; i < HPAGE_PMD_NR; i++) > >+ atomic_dec(&page[i]._mapcount); > >+ } > >+ } else if (!TestSetPageDoubleMap(page)) { > >+ /* > >+ * The first PMD split for the compound page and we still > >+ * have other PMD mapping of the page: bump _mapcount in > >+ * every small page. > >+ * This reference will go away with last compound_mapcount. > >+ */ > >+ for (i = 0; i < HPAGE_PMD_NR; i++) > >+ atomic_inc(&page[i]._mapcount); > > The order of actions here means that between TestSetPageDoubleMap() and the > atomic incs, anyone calling page_mapcount() on one of the pages not > processed by the for loop yet, will see a value lower by 1 from what he > should see. I wonder if that can cause any trouble somewhere, especially if > there's only one other compound mapping and page_mapcount() will return 0 > instead of 1? Good catch. Thanks. What about this? diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 0f1f5731a893..cd0e6addb662 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2636,15 +2636,25 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, for (i = 0; i < HPAGE_PMD_NR; i++) atomic_dec(&page[i]._mapcount); } - } else if (!TestSetPageDoubleMap(page)) { + } else if (!PageDoubleMap(page)) { /* * The first PMD split for the compound page and we still * have other PMD mapping of the page: bump _mapcount in * every small page. + * * This reference will go away with last compound_mapcount. + * + * Note, we need to increment mapcounts before setting + * PG_double_map to avoid false-negative page_mapped(). */ for (i = 0; i < HPAGE_PMD_NR; i++) atomic_inc(&page[i]._mapcount); + + if (TestSetPageDoubleMap(page)) { + /* Race with another __split_huge_pmd() for the page */ + for (i = 0; i < HPAGE_PMD_NR; i++) + atomic_dec(&page[i]._mapcount); + } } smp_wmb(); /* make pte visible before pmd */ > Conversely, when clearing PageDoubleMap() above (or in one of those rmap > functions IIRC), one could see mapcount inflated by one. But I guess that's > less dangerous. I think it's safe. -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/
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From: "Kirill A. Shutemov" <kirill@shutemov.name> To: Vlastimil Babka <vbabka@suse.cz> 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 29/36] thp: implement split_huge_pmd() Date: Mon, 22 Jun 2015 14:14:34 +0300 [thread overview] Message-ID: <20150622111434.GC7934@node.dhcp.inet.fi> (raw) In-Reply-To: <557959BC.5000303@suse.cz> On Thu, Jun 11, 2015 at 11:49:48AM +0200, Vlastimil Babka wrote: > On 06/03/2015 07:06 PM, Kirill A. Shutemov wrote: > >Original split_huge_page() combined two operations: splitting PMDs into > >tables of PTEs and splitting underlying compound page. This patch > >implements split_huge_pmd() which split given PMD without splitting > >other PMDs this page mapped with or underlying compound page. > > > >Without tail page refcounting, implementation of split_huge_pmd() is > >pretty straight-forward. > > > >Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > >Tested-by: Sasha Levin <sasha.levin@oracle.com> > > [...] > > >+ > >+ if (atomic_add_negative(-1, compound_mapcount_ptr(page))) { > >+ /* Last compound_mapcount is gone. */ > >+ __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES); > >+ if (PageDoubleMap(page)) { > >+ /* No need in mapcount reference anymore */ > >+ ClearPageDoubleMap(page); > >+ for (i = 0; i < HPAGE_PMD_NR; i++) > >+ atomic_dec(&page[i]._mapcount); > >+ } > >+ } else if (!TestSetPageDoubleMap(page)) { > >+ /* > >+ * The first PMD split for the compound page and we still > >+ * have other PMD mapping of the page: bump _mapcount in > >+ * every small page. > >+ * This reference will go away with last compound_mapcount. > >+ */ > >+ for (i = 0; i < HPAGE_PMD_NR; i++) > >+ atomic_inc(&page[i]._mapcount); > > The order of actions here means that between TestSetPageDoubleMap() and the > atomic incs, anyone calling page_mapcount() on one of the pages not > processed by the for loop yet, will see a value lower by 1 from what he > should see. I wonder if that can cause any trouble somewhere, especially if > there's only one other compound mapping and page_mapcount() will return 0 > instead of 1? Good catch. Thanks. What about this? diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 0f1f5731a893..cd0e6addb662 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2636,15 +2636,25 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, for (i = 0; i < HPAGE_PMD_NR; i++) atomic_dec(&page[i]._mapcount); } - } else if (!TestSetPageDoubleMap(page)) { + } else if (!PageDoubleMap(page)) { /* * The first PMD split for the compound page and we still * have other PMD mapping of the page: bump _mapcount in * every small page. + * * This reference will go away with last compound_mapcount. + * + * Note, we need to increment mapcounts before setting + * PG_double_map to avoid false-negative page_mapped(). */ for (i = 0; i < HPAGE_PMD_NR; i++) atomic_inc(&page[i]._mapcount); + + if (TestSetPageDoubleMap(page)) { + /* Race with another __split_huge_pmd() for the page */ + for (i = 0; i < HPAGE_PMD_NR; i++) + atomic_dec(&page[i]._mapcount); + } } smp_wmb(); /* make pte visible before pmd */ > Conversely, when clearing PageDoubleMap() above (or in one of those rmap > functions IIRC), one could see mapcount inflated by one. But I guess that's > less dangerous. I think it's safe. -- Kirill A. Shutemov -- 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 11:15 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 [this message] 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 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
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