From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
Dave Hansen <dave.hansen@intel.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>,
Jerome Marchand <jmarchan@redhat.com>,
Sasha Levin <sasha.levin@oracle.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/3] thp: change deferred_split_count() to return number of THP in queue
Date: Fri, 22 Jan 2016 17:20:50 +0200 [thread overview]
Message-ID: <20160122152049.GA24420@node.shutemov.name> (raw)
In-Reply-To: <20160122143127.GI7119@redhat.com>
On Fri, Jan 22, 2016 at 03:31:27PM +0100, Andrea Arcangeli wrote:
> On Thu, Jan 21, 2016 at 03:09:22PM +0300, Kirill A. Shutemov wrote:
> > @@ -3511,7 +3506,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
> > list_splice_tail(&list, &pgdata->split_queue);
> > spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
> >
> > - return split * HPAGE_PMD_NR / 2;
> > + return split;
> > }
>
> Looking further at how the caller processes this "split" retval, if
> the list has been fully shrunk by the page freeing, between the
> split_count and split_scan, the caller seems to ignore a 0 value
> returned above and it'll keep calling even if sc->nr_to_scan isn't
> decreasing. The caller won't even check sc->nr_to_scan to notice that
> it isn't decreasing anymore, it's write-only as far as the caller is
> concerned.
>
> It's also weird we can't return the number of freed pages and break
> the loop with just one invocation of the split_scan, but that's a
> slight inefficiency in the caller interface. The caller also seems to
> forget to set total_scan to 0 if SHRINK_STOP was returned but perhaps
> that's on purpose, however for our purpose it'd be better off if it
> did.
>
> The split_queue.next is going to be hot in the CPU cache anyway, so
> unless we change the caller, it should be worth it to add a list_empty
> check and return SHRINK_STOP if it was empty. Doing it at the start or
> end doesn't make much difference, at the end lockless it'll deal with
> the split failures too if any.
>
> return split ? : list_empty(&pgdat->split_queue) ? SPLIT_STOP : 0;
Ughh. Shrinker interface is confusing.
next prev parent reply other threads:[~2016-01-22 15:20 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-06 15:23 [PATCHv12 00/37] THP refcounting redesign Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 01/37] mm, proc: adjust PSS calculation Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 02/37] rmap: add argument to charge compound page Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 03/37] memcg: adjust to support new THP refcounting Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 04/37] mm, thp: adjust conditions when we can reuse the page on WP fault Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 05/37] mm: adjust FOLL_SPLIT for new refcounting Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 06/37] mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 07/37] thp, mlock: do not allow huge pages in mlocked area Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 08/37] khugepaged: ignore pmd tables with THP mapped with ptes Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 09/37] thp: rename split_huge_page_pmd() to split_huge_pmd() Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 10/37] mm, vmstats: new THP splitting event Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 11/37] mm: temporally mark THP broken Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 12/37] thp: drop all split_huge_page()-related code Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 13/37] mm: drop tail page refcounting Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 14/37] futex, thp: remove special case for THP in get_futex_key Kirill A. Shutemov
2015-10-22 8:24 ` Artem Savkov
2015-10-22 9:49 ` Kirill A. Shutemov
2015-10-22 10:33 ` Artem Savkov
2015-10-06 15:23 ` [PATCHv12 15/37] ksm: prepare to new THP semantics Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 16/37] mm, thp: remove compound_lock Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 17/37] arm64, thp: remove infrastructure for handling splitting PMDs Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 18/37] arm, " Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 19/37] mips, " Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 20/37] powerpc, " Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 21/37] s390, " Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 22/37] sparc, " Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 23/37] tile, " Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 24/37] x86, " Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 25/37] mm, " Kirill A. Shutemov
2015-10-08 8:52 ` Vineet Gupta
2015-10-09 9:25 ` Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 26/37] mm: rework mapcount accounting to enable 4k mapping of THPs Kirill A. Shutemov
2015-10-27 6:18 ` Naoya Horiguchi
2015-10-27 9:30 ` Kirill A. Shutemov
2015-10-27 23:24 ` Naoya Horiguchi
2015-10-29 21:50 ` Kirill A. Shutemov
2015-10-30 8:33 ` Naoya Horiguchi
2015-10-29 8:19 ` Naoya Horiguchi
2015-10-29 21:20 ` Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 27/37] mm: differentiate page_mapped() from page_mapcount() for compound pages Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 28/37] mm, numa: skip PTE-mapped THP on numa fault Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 29/37] thp: implement split_huge_pmd() Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 30/37] thp: add option to setup migration entries during PMD split Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 31/37] thp, mm: split_huge_page(): caller need to lock page Kirill A. Shutemov
2015-10-06 15:23 ` [PATCHv12 32/37] thp: reintroduce split_huge_page() Kirill A. Shutemov
2015-11-18 16:24 ` Sasha Levin
2015-11-18 19:05 ` Kirill A. Shutemov
2015-11-27 4:26 ` Sasha Levin
2015-10-06 15:24 ` [PATCHv12 33/37] migrate_pages: try to split pages on qeueuing Kirill A. Shutemov
2015-10-06 15:24 ` [PATCHv12 34/37] thp: introduce deferred_split_huge_page() Kirill A. Shutemov
2016-01-21 1:22 ` Andrea Arcangeli
2016-01-21 12:09 ` [PATCH 0/3] Couple of fixes for deferred_split_huge_page() Kirill A. Shutemov
2016-01-21 12:09 ` [PATCH 1/3] thp: make split_queue per-node Kirill A. Shutemov
2016-01-21 12:09 ` [PATCH 2/3] thp: change deferred_split_count() to return number of THP in queue Kirill A. Shutemov
2016-01-22 14:31 ` Andrea Arcangeli
2016-01-22 15:20 ` Kirill A. Shutemov [this message]
2016-01-21 12:09 ` [PATCH 3/3] thp: limit number of object to scan on deferred_split_scan() Kirill A. Shutemov
2016-02-04 13:11 ` Kirill A. Shutemov
2016-01-21 22:52 ` [PATCH 0/3] Couple of fixes for deferred_split_huge_page() Andrea Arcangeli
2015-10-06 15:24 ` [PATCHv12 35/37] mm: re-enable THP Kirill A. Shutemov
2015-10-06 15:24 ` [PATCHv12 36/37] thp: update documentation Kirill A. Shutemov
2015-10-06 15:24 ` [PATCHv12 37/37] thp: allow mlocked THP again Kirill A. Shutemov
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