* [PATCH] mm/swapfile: add cond_resched() in get_swap_pages()
@ 2023-01-28 9:47 Longlong Xia
2023-01-29 0:39 ` Huang, Ying
2023-01-29 21:03 ` Andrew Morton
0 siblings, 2 replies; 6+ messages in thread
From: Longlong Xia @ 2023-01-28 9:47 UTC (permalink / raw)
To: akpm
Cc: linux-mm, linux-kernel, ying.huang, chenwandun, wangkefeng.wang,
sunnanyong, Longlong Xia
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@huawei.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
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH] mm/swapfile: add cond_resched() in get_swap_pages()
2023-01-28 9:47 [PATCH] mm/swapfile: add cond_resched() in get_swap_pages() Longlong Xia
@ 2023-01-29 0:39 ` Huang, Ying
2023-01-29 21:03 ` Andrew Morton
1 sibling, 0 replies; 6+ messages in thread
From: Huang, Ying @ 2023-01-29 0:39 UTC (permalink / raw)
To: Longlong Xia
Cc: akpm, linux-mm, linux-kernel, chenwandun, wangkefeng.wang, sunnanyong
Longlong Xia <xialonglong1@huawei.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@huawei.com>
Looks good to me. Thanks!
Reviewed-by: "Huang, Ying" <ying.huang@intel.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:
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] mm/swapfile: add cond_resched() in get_swap_pages()
2023-01-28 9:47 [PATCH] mm/swapfile: add cond_resched() in get_swap_pages() Longlong Xia
2023-01-29 0:39 ` Huang, Ying
@ 2023-01-29 21:03 ` Andrew Morton
2023-01-30 0:26 ` Huang, Ying
1 sibling, 1 reply; 6+ messages in thread
From: Andrew Morton @ 2023-01-29 21:03 UTC (permalink / raw)
To: Longlong Xia
Cc: linux-mm, linux-kernel, ying.huang, chenwandun, wangkefeng.wang,
sunnanyong
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?
I'm thinking this fix should be backported into -stable kernels.
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] mm/swapfile: add cond_resched() in get_swap_pages()
2023-01-29 21:03 ` Andrew Morton
@ 2023-01-30 0:26 ` Huang, Ying
2023-01-31 7:10 ` [PATCH -next] mm/swapfile: remove pr_debug " Longlong Xia
0 siblings, 1 reply; 6+ messages in thread
From: Huang, Ying @ 2023-01-30 0:26 UTC (permalink / raw)
To: Andrew Morton
Cc: Longlong Xia, linux-mm, linux-kernel, chenwandun,
wangkefeng.wang, sunnanyong
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
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH -next] mm/swapfile: remove pr_debug in get_swap_pages()
2023-01-30 0:26 ` Huang, Ying
@ 2023-01-31 7:10 ` Longlong Xia
2023-01-31 7:27 ` Huang, Ying
0 siblings, 1 reply; 6+ messages in thread
From: Longlong Xia @ 2023-01-31 7:10 UTC (permalink / raw)
To: akpm
Cc: linux-mm, linux-kernel, ying.huang, chenwandun, wangkefeng.wang,
sunnanyong, Longlong Xia
It's known that get_swap_pages() may fail to find available space
under some extreme case, but pr_debug() provides useless information.
Let's remove it.
Signed-off-by: Longlong Xia <xialonglong1@huawei.com>
---
mm/swapfile.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6202a6668a63..99143875d6f0 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1098,8 +1098,6 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
spin_unlock(&si->lock);
if (n_ret || size == SWAPFILE_CLUSTER)
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);
--
2.25.1
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH -next] mm/swapfile: remove pr_debug in get_swap_pages()
2023-01-31 7:10 ` [PATCH -next] mm/swapfile: remove pr_debug " Longlong Xia
@ 2023-01-31 7:27 ` Huang, Ying
0 siblings, 0 replies; 6+ messages in thread
From: Huang, Ying @ 2023-01-31 7:27 UTC (permalink / raw)
To: Longlong Xia
Cc: akpm, linux-mm, linux-kernel, chenwandun, wangkefeng.wang, sunnanyong
Longlong Xia <xialonglong1@huawei.com> writes:
> It's known that get_swap_pages() may fail to find available space
> under some extreme case, but pr_debug() provides useless information.
> Let's remove it.
>
> Signed-off-by: Longlong Xia <xialonglong1@huawei.com>
Thanks!
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
> ---
> mm/swapfile.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 6202a6668a63..99143875d6f0 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1098,8 +1098,6 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
> spin_unlock(&si->lock);
> if (n_ret || size == SWAPFILE_CLUSTER)
> 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);
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2023-01-31 7:28 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2023-01-28 9:47 [PATCH] mm/swapfile: add cond_resched() in get_swap_pages() Longlong Xia
2023-01-29 0:39 ` Huang, Ying
2023-01-29 21:03 ` Andrew Morton
2023-01-30 0:26 ` Huang, Ying
2023-01-31 7:10 ` [PATCH -next] mm/swapfile: remove pr_debug " Longlong Xia
2023-01-31 7:27 ` Huang, Ying
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