linux-kernel - Re: [PATCH] shmem: avoid huge pages for small files

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Message-ID: <20161017141245.GC27459@dhcp22.suse.cz>
Date:   Mon, 17 Oct 2016 16:12:46 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] shmem: avoid huge pages for small files

On Mon 17-10-16 15:30:21, Kirill A. Shutemov wrote:
[...]
> >From fd0b01b9797ddf2bef308c506c42d3dd50f11793 Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Date: Mon, 17 Oct 2016 14:44:47 +0300
> Subject: [PATCH] shmem: avoid huge pages for small files
> 
> Huge pages are detrimental for small file: they causes noticible
> overhead on both allocation performance and memory footprint.
> 
> This patch aimed to address this issue by avoiding huge pages until file
> grown to specified size. This would cover most of the cases where huge
> pages causes regressions in performance.
> 
> By default the minimal file size to allocate huge pages is equal to size
> of huge page.

ok

> We add two handle to specify minimal file size for huge pages:
> 
>   - mount option 'huge_min_size';
> 
>   - sysfs file /sys/kernel/mm/transparent_hugepage/shmem_min_size for
>     in-kernel tmpfs mountpoint;

Could you explain who might like to change the minimum value (other than
disable the feautre for the mount point) and for what reason?

[...]

> @@ -238,6 +238,12 @@ values:
>    - "force":
>      Force the huge option on for all - very useful for testing;
>  
> +Tehre's limit on minimal file size before kenrel starts allocate huge
> +pages for it. By default it's size of huge page.

Smoe tyopse
-- 
Michal Hocko
SUSE Labs