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Message-ID: <20171011122948.amcbow6w64eidkfq@dhcp22.suse.cz>
Date: Wed, 11 Oct 2017 14:29:48 +0200
From: Michal Hocko <mhocko@...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>,
Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH -mm -v2] mm, swap: Use page-cluster as max window of VMA
based swap readahead
On Wed 11-10-17 15:08:47, 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>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
Thanks for addressing this issue.
Acked-by: Michal Hocko <mhocko@...e.com>
> ---
> Documentation/ABI/testing/sysfs-kernel-mm-swap | 10 -------
> mm/swap_state.c | 41 +++++---------------------
> 2 files changed, 7 insertions(+), 44 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..05b6803f0cce 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
> @@ -664,6 +660,13 @@ struct page *swap_readahead_detect(struct vm_fault *vmf,
> pte_t *tpte;
> #endif
>
> + max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
> + SWAP_RA_ORDER_CEILING);
> + if (max_win == 1) {
> + swap_ra->win = 1;
> + return NULL;
> + }
> +
> faddr = vmf->address;
> entry = pte_to_swp_entry(vmf->orig_pte);
> if ((unlikely(non_swap_entry(entry))))
> @@ -672,12 +675,6 @@ struct page *swap_readahead_detect(struct vm_fault *vmf,
> if (page)
> return page;
>
> - max_win = 1 << READ_ONCE(swap_ra_max_order);
> - if (max_win == 1) {
> - swap_ra->win = 1;
> - return NULL;
> - }
> -
> fpfn = PFN_DOWN(faddr);
> swap_ra_info = GET_SWAP_RA_VAL(vma);
> pfn = PFN_DOWN(SWAP_RA_ADDR(swap_ra_info));
> @@ -786,32 +783,8 @@ static struct kobj_attribute vma_ra_enabled_attr =
> __ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,
> vma_ra_enabled_store);
>
> -static ssize_t vma_ra_max_order_show(struct kobject *kobj,
> - struct kobj_attribute *attr, char *buf)
> -{
> - return sprintf(buf, "%d\n", swap_ra_max_order);
> -}
> -static ssize_t vma_ra_max_order_store(struct kobject *kobj,
> - struct kobj_attribute *attr,
> - const char *buf, size_t count)
> -{
> - int err, v;
> -
> - err = kstrtoint(buf, 10, &v);
> - if (err || v > SWAP_RA_ORDER_CEILING || v <= 0)
> - return -EINVAL;
> -
> - swap_ra_max_order = v;
> -
> - return count;
> -}
> -static struct kobj_attribute vma_ra_max_order_attr =
> - __ATTR(vma_ra_max_order, 0644, vma_ra_max_order_show,
> - vma_ra_max_order_store);
> -
> static struct attribute *swap_attrs[] = {
> &vma_ra_enabled_attr.attr,
> - &vma_ra_max_order_attr.attr,
> NULL,
> };
>
> --
> 2.14.2
>
> --
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--
Michal Hocko
SUSE Labs
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