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 36/36] thp: update documentation Date: Mon, 22 Jun 2015 16:18:27 +0300 [thread overview] Message-ID: <20150622131827.GF7934@node.dhcp.inet.fi> (raw) In-Reply-To: <55797F57.8040001@suse.cz> 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. > >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? 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. -- 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 36/36] thp: update documentation Date: Mon, 22 Jun 2015 16:18:27 +0300 [thread overview] Message-ID: <20150622131827.GF7934@node.dhcp.inet.fi> (raw) In-Reply-To: <55797F57.8040001@suse.cz> 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. > >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? 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. -- 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 13:19 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 [this message] 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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