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

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Date:   Sat, 28 Jan 2023 09:47:57 +0000
From:   Longlong Xia <xialonglong1@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <ying.huang@...el.com>, <chenwandun@...wei.com>,
        <wangkefeng.wang@...wei.com>, <sunnanyong@...wei.com>,
        Longlong Xia <xialonglong1@...wei.com>
Subject: [PATCH] mm/swapfile: add cond_resched() in get_swap_pages()

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>
---
 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:
-- 
2.25.1