linux-kernel - Re: [PATCH] mm/swapfile: add cond_resched() in get_swap

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Message-ID: <87a622cgxy.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Sun, 29 Jan 2023 08:39:21 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Longlong Xia <xialonglong1@...wei.com>
Cc:     <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <chenwandun@...wei.com>,
        <wangkefeng.wang@...wei.com>, <sunnanyong@...wei.com>
Subject: Re: [PATCH] mm/swapfile: add cond_resched() in get_swap_pages()

Longlong Xia <xialonglong1@...wei.com> writes:

> The softlockup still occurs in get_swap_pages() under memory pressure.
> 64 CPU cores, 64GB memory, and 28 zram devices, the disksize of each
> zram device is 50MB with same priority as si. Use the stress-ng tool
> to increase memory pressure, causing the system to oom frequently.
>
> The plist_for_each_entry_safe() loops in get_swap_pages() could reach
> tens of thousands of times to find available space (extreme case:
> cond_resched() is not called in scan_swap_map_slots()). Let's add
> cond_resched() into get_swap_pages() when failed to find available
> space to avoid softlockup.
>
> Signed-off-by: Longlong Xia <xialonglong1@...wei.com>

Looks good to me. Thanks!

Reviewed-by: "Huang, Ying" <ying.huang@...el.com>

> ---
>  mm/swapfile.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 908a529bca12..4fa440e87cd6 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1100,6 +1100,7 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
>  			goto check_out;
>  		pr_debug("scan_swap_map of si %d failed to find offset\n",
>  			si->type);
> +		cond_resched();
>  
>  		spin_lock(&swap_avail_lock);
>  nextsi: