| Message ID | 20230128094757.1060525-1-xialonglong1@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/swapfile: add cond_resched() in get_swap_pages() | expand |
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:
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.
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
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:
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(+)