Messages in this thread | | | From | "Huang, Ying" <> | Subject | Re: [PATCH] mm/swapfile: add cond_resched() in get_swap_pages() | Date | Mon, 30 Jan 2023 08:26:41 +0800 |
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Andrew Morton <akpm@linux-foundation.org> writes:
> On Sat, 28 Jan 2023 09:47:57 +0000 Longlong Xia <xialonglong1@huawei.com> wrote: > >> 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. >> >> ... >> >> --- 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: > > This must be pretty rare? My googling for "scan_swap_map of si %d > failed to find offset" turns up zero reports, but I guess few people > enable pr_debug. > > I wonder if we should remove that pr_debug(). I mean, it's known that > this happens, what value does the printk add?
Sounds reasonable to me. And if we want to debug, we can use bpf too.
> I'm thinking this fix should be backported into -stable kernels.
Best Regards, Huang, Ying
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