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

From: Michal Hocko
Date: Mon Oct 24 2016 - 08:43:48 EST


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@xxxxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
> 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