On Wed, Oct 11, 2017 at 03:08:47PM +0800, Huang, Ying wrote:
> From: Huang Ying <ying.huang@xxxxxxxxx>
>
> 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@xxxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Shaohua Li <shli@xxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
> Cc: Tim Chen <tim.c.chen@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Reported-by: Minchan Kim <minchan@xxxxxxxxxx>
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Below a question:
> ---
> 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@xxxxxxxxx>
> -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);
Why do we need READ_ONCE in here? IOW, without it, what happens?
> + if (max_win == 1) {
> + swap_ra->win = 1;
> + return NULL;
> + }
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