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From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Ning Qu <quning@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 00/24] huge tmpfs: an alternative approach to THPageCache
Date: Mon, 23 Feb 2015 15:48:10 +0200	[thread overview]
Message-ID: <20150223134810.GB7322@node.dhcp.inet.fi> (raw)
In-Reply-To: <alpine.LSU.2.11.1502201941340.14414@eggly.anvils>

On Fri, Feb 20, 2015 at 07:49:16PM -0800, Hugh Dickins wrote:
> I warned last month that I have been working on "huge tmpfs":
> an implementation of Transparent Huge Page Cache in tmpfs,
> for those who are tired of the limitations of hugetlbfs.
> 
> Here's a fully working patchset, against v3.19 so that you can give it
> a try against a stable base.  I've not yet studied how well it applies
> to current git: probably lots of easily resolved clashes with nonlinear
> removal.  Against mmotm, the rmap.c differences looked nontrivial.
> 
> Fully working?  Well, at present page migration just keeps away from
> these teams of pages.  And once memory pressure has disbanded a team
> to swap it out, there is nothing to put it together again later on,
> to restore the original hugepage performance.  Those must follow,
> but no thought yet (khugepaged? maybe).
> 
> Yes, I realize there's nothing yet under Documentation, nor fs/proc
> beyond meminfo, nor other debug/visibility files: must follow, but
> I've cared more to provide the basic functionality.
> 
> I don't expect to update this patchset in the next few weeks: now that
> it's posted, my priority is look at other people's work before LSF/MM;
> and in particular, of course, your (Kirill's) THP refcounting redesign.

I scanned through the patches to get general idea on how it works. I'm not
sure that I will have time and will power to do proper code-digging before
the summit. I found few bugs in my patchset which I want to troubleshoot
first.

One thing I'm not really comfortable with is introducing yet another way
to couple pages together. It's less risky in short term than my approach
-- fewer existing codepaths affected, but it rises maintaining cost later.
Not sure it's what we want.

After Johannes' work which added exceptional entries to normal page cache
I hoped to see shmem/tmpfs implementation moving toward generic page
cache. But this patchset is step in other direction -- it makes
shmem/tmpfs even more special-cased. :(

Do you have any insights on how this approach applies to real filesystems?
I don't think there's any show stopper, but better to ask early ;)

-- 
 Kirill A. Shutemov

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  parent reply	other threads:[~2015-02-23 13:48 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-21  3:49 [PATCH 00/24] huge tmpfs: an alternative approach to THPageCache Hugh Dickins
2015-02-21  3:51 ` [PATCH 01/24] mm: update_lru_size warn and reset bad lru_size Hugh Dickins
2015-02-23  9:30   ` Kirill A. Shutemov
2015-03-23  2:44     ` Hugh Dickins
2015-02-21  3:54 ` [PATCH 02/24] mm: update_lru_size do the __mod_zone_page_state Hugh Dickins
2015-02-21  3:56 ` [PATCH 03/24] mm: use __SetPageSwapBacked and don't ClearPageSwapBacked Hugh Dickins
2015-02-25 10:53   ` Mel Gorman
2015-03-23  3:01     ` Hugh Dickins
2015-02-21  3:58 ` [PATCH 04/24] mm: make page migration's newpage handling more robust Hugh Dickins
2015-02-21  4:00 ` [PATCH 05/24] tmpfs: preliminary minor tidyups Hugh Dickins
2015-02-21  4:01 ` [PATCH 06/24] huge tmpfs: prepare counts in meminfo, vmstat and SysRq-m Hugh Dickins
2015-02-21  4:03 ` [PATCH 07/24] huge tmpfs: include shmem freeholes in available memory counts Hugh Dickins
2015-02-21  4:05 ` [PATCH 08/24] huge tmpfs: prepare huge=N mount option and /proc/sys/vm/shmem_huge Hugh Dickins
2015-02-21  4:06 ` [PATCH 09/24] huge tmpfs: try to allocate huge pages, split into a team Hugh Dickins
2015-02-21  4:07 ` [PATCH 10/24] huge tmpfs: avoid team pages in a few places Hugh Dickins
2015-02-21  4:09 ` [PATCH 11/24] huge tmpfs: shrinker to migrate and free underused holes Hugh Dickins
2015-03-19 16:56   ` Konstantin Khlebnikov
2015-03-23  4:40     ` Hugh Dickins
2015-03-23 12:50       ` Kirill A. Shutemov
2015-03-23 13:50         ` Kirill A. Shutemov
2015-03-24 12:57       ` Kirill A. Shutemov
2015-03-25  0:41         ` Hugh Dickins
2015-02-21  4:11 ` [PATCH 12/24] huge tmpfs: get_unmapped_area align and fault supply huge page Hugh Dickins
2015-02-21  4:12 ` [PATCH 13/24] huge tmpfs: extend get_user_pages_fast to shmem pmd Hugh Dickins
2015-02-21  4:13 ` [PATCH 14/24] huge tmpfs: extend vma_adjust_trans_huge " Hugh Dickins
2015-02-21  4:15 ` [PATCH 15/24] huge tmpfs: rework page_referenced_one and try_to_unmap_one Hugh Dickins
2015-02-21  4:16 ` [PATCH 16/24] huge tmpfs: fix problems from premature exposure of pagetable Hugh Dickins
2015-07-01 10:53   ` Kirill A. Shutemov
2015-02-21  4:18 ` [PATCH 17/24] huge tmpfs: map shmem by huge page pmd or by page team ptes Hugh Dickins
2015-02-21  4:20 ` [PATCH 18/24] huge tmpfs: mmap_sem is unlocked when truncation splits huge pmd Hugh Dickins
2015-02-21  4:22 ` [PATCH 19/24] huge tmpfs: disband split huge pmds on race or memory failure Hugh Dickins
2015-02-21  4:23 ` [PATCH 20/24] huge tmpfs: use Unevictable lru with variable hpage_nr_pages() Hugh Dickins
2015-02-21  4:25 ` [PATCH 21/24] huge tmpfs: fix Mlocked meminfo, tracking huge and unhuge mlocks Hugh Dickins
2015-02-21  4:27 ` [PATCH 22/24] huge tmpfs: fix Mapped meminfo, tracking huge and unhuge mappings Hugh Dickins
2015-02-21  4:29 ` [PATCH 23/24] kvm: plumb return of hva when resolving page fault Hugh Dickins
2015-02-21  4:31 ` [PATCH 24/24] kvm: teach kvm to map page teams as huge pages Hugh Dickins
2015-02-23 13:48 ` Kirill A. Shutemov [this message]
2015-03-23  2:25   ` [PATCH 00/24] huge tmpfs: an alternative approach to THPageCache Hugh Dickins

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