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Message-ID: <20171010082040.GA16508@bbox>
Date: Tue, 10 Oct 2017 17:20:40 +0900
From: Minchan Kim <minchan@...nel.org>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
Rik van Riel <riel@...hat.com>, Shaohua Li <shli@...nel.org>,
Hugh Dickins <hughd@...gle.com>,
Fengguang Wu <fengguang.wu@...el.com>,
Tim Chen <tim.c.chen@...el.com>,
Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH -mm] mm, swap: Use page-cluster as max window of VMA
based swap readahead
On Tue, Oct 10, 2017 at 02:08:55PM +0800, Huang, Ying wrote:
> From: Huang Ying <ying.huang@...el.com>
>
> When the VMA based swap readahead was introduced, a new knob
>
> /sys/kernel/mm/swap/vma_ra_max_order
>
> was added as the max window of VMA swap readahead. This is to make it
> possible to use different max window for VMA based readahead and
> original physical readahead. But Minchan Kim pointed out that this
> will cause a regression because setting page-cluster sysctl to zero
> cannot disable swap readahead with the change.
>
> To fix the regression, the page-cluster sysctl is used as the max
> window of both the VMA based swap readahead and original physical swap
> readahead. If more fine grained control is needed in the future, more
> knobs can be added as the subordinate knobs of the page-cluster
> sysctl.
>
> The vma_ra_max_order knob is deleted. Because the knob was
> introduced in v4.14-rc1, and this patch is targeting being merged
> before v4.14 releasing, there should be no existing users of this
> newly added ABI.
>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Shaohua Li <shli@...nel.org>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Fengguang Wu <fengguang.wu@...el.com>
> Cc: Tim Chen <tim.c.chen@...el.com>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Reported-by: Minchan Kim <minchan@...nel.org>
It seems your script is Ccing only with Cc: tag, not other tags.
Fix it so any participant of topic can get the mail.
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> ---
> Documentation/ABI/testing/sysfs-kernel-mm-swap | 10 ---------
> mm/swap_state.c | 31 ++------------------------
> 2 files changed, 2 insertions(+), 39 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-swap b/Documentation/ABI/testing/sysfs-kernel-mm-swap
> index 587db52084c7..94672016c268 100644
> --- a/Documentation/ABI/testing/sysfs-kernel-mm-swap
> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-swap
> @@ -14,13 +14,3 @@ Description: Enable/disable VMA based swap readahead.
> still used for tmpfs etc. other users. If set to
> false, the global swap readahead algorithm will be
> used for all swappable pages.
> -
> -What: /sys/kernel/mm/swap/vma_ra_max_order
> -Date: August 2017
> -Contact: Linux memory management mailing list <linux-mm@...ck.org>
> -Description: The max readahead size in order for VMA based swap readahead
> -
> - VMA based swap readahead algorithm will readahead at
> - most 1 << max_order pages for each readahead. The
> - real readahead size for each readahead will be scaled
> - according to the estimation algorithm.
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index ed91091d1e68..4d01ecff62d9 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -39,10 +39,6 @@ struct address_space *swapper_spaces[MAX_SWAPFILES];
> static unsigned int nr_swapper_spaces[MAX_SWAPFILES];
> bool swap_vma_readahead = true;
>
> -#define SWAP_RA_MAX_ORDER_DEFAULT 3
> -
> -static int swap_ra_max_order = SWAP_RA_MAX_ORDER_DEFAULT;
> -
> #define SWAP_RA_WIN_SHIFT (PAGE_SHIFT / 2)
> #define SWAP_RA_HITS_MASK ((1UL << SWAP_RA_WIN_SHIFT) - 1)
> #define SWAP_RA_HITS_MAX SWAP_RA_HITS_MASK
> @@ -672,7 +668,8 @@ struct page *swap_readahead_detect(struct vm_fault *vmf,
> if (page)
> return page;
>
> - max_win = 1 << READ_ONCE(swap_ra_max_order);
> + max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
> + SWAP_RA_ORDER_CEILING);
Why doesn't you check it in swap_use_vma_readahead in my original patch?
My purpose in there is to avoid unnecessary function call and
lookup_swap_cache in there.
If you really want to do that in swap_readahead_detect itself, please
move above routine to ahead of faddr = vmf->address to avoid unncessary
instructions.
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