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Message-ID: <87r2ubo08t.fsf@yhuang-dev.intel.com>
Date: Tue, 10 Oct 2017 16:50:10 +0800
From: "Huang\, Ying" <ying.huang@...el.com>
To: Minchan Kim <minchan@...nel.org>
Cc: "Huang\, Ying" <ying.huang@...el.com>,
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
Minchan Kim <minchan@...nel.org> writes:
> 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.
I just used `git send-email`, no other scripts. We need to fix `git send-email`?
>> 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.
Although the avoided instructions is just a few, I can move the max
window checking as the first statements in the function.
Best Regards,
Huang, Ying
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