linux-kernel - Re: [PATCHv4] shmem: avoid huge pages for small files

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Message-ID: <20161024124337.GA17103@dhcp22.suse.cz>
Date:   Mon, 24 Oct 2016 14:43:37 +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>,
        Dave Chinner <david@...morbit.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4] shmem: avoid huge pages for small files

On Sat 22-10-16 01:46:29, Kirill A. Shutemov wrote:
> On Fri, Oct 21, 2016 at 09:51:03PM +0300, Kirill A. Shutemov wrote:
> > +		case SHEME_HUGE_ALWAYS:
> 
> Oops. Forgot to commit the fixup :-/
> 
> >From 79b0a3bf4503225d0e6ba553b8496f0c4d55514e 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: [PATCHv4] 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 size of huge page. This would cover most of the cases where huge
> pages causes regressions in performance.
> 
> Couple notes:
> 
>   - if shmem_enabled is set to 'force', the limit is ignored. We still
>     want to generate as many pages as possible for functional testing.
> 
>   - the limit doesn't affect khugepaged behaviour: it still can collapse
>     pages based on its settings;
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  Documentation/vm/transhuge.txt | 3 +++
>  mm/shmem.c                     | 5 +++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
> index 2ec6adb5a4ce..d1889c7c8c46 100644
> --- a/Documentation/vm/transhuge.txt
> +++ b/Documentation/vm/transhuge.txt
> @@ -238,6 +238,9 @@ values:
>    - "force":
>      Force the huge option on for all - very useful for testing;
>  
> +To avoid overhead for small files, we don't allocate huge pages for a file
> +until it grows to size of huge pages.
> +
>  == Need of application restart ==
>  
>  The transparent_hugepage/enabled values and tmpfs mount option only affect
> diff --git a/mm/shmem.c b/mm/shmem.c
> index ad7813d73ea7..49618d2d6330 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1692,6 +1692,11 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
>  				goto alloc_huge;
>  			/* TODO: implement fadvise() hints */
>  			goto alloc_nohuge;
> +		case SHMEM_HUGE_ALWAYS:
> +			i_size = i_size_read(inode);
> +			if (index < HPAGE_PMD_NR && i_size < HPAGE_PMD_SIZE)
> +				goto alloc_nohuge;
> +			break;
>  		}
>  
>  alloc_huge:
> -- 
>  Kirill A. Shutemov

-- 
Michal Hocko
SUSE Labs