| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <40632FBD-8874-4B6C-A945-F2EBC96CF12B@fb.com>
Date: Thu, 6 May 2021 00:54:59 +0000
From: Roman Gushchin <guro@...com>
To: kernel test robot <oliver.sang@...el.com>
CC: Dennis Zhou <dennis@...nel.org>,
Pratik Sampat <psampat@...ux.ibm.com>,
LKML <linux-kernel@...r.kernel.org>,
"lkp@...ts.01.org" <lkp@...ts.01.org>,
"lkp@...el.com" <lkp@...el.com>,
"ying.huang@...el.com" <ying.huang@...el.com>,
"feng.tang@...el.com" <feng.tang@...el.com>,
"zhengjun.xing@...el.com" <zhengjun.xing@...el.com>
Subject: Re: [percpu] ace7e70901: aim9.sync_disk_rw.ops_per_sec -2.3%
regression
Ping
> On Apr 29, 2021, at 18:25, Roman Gushchin <guro@...com> wrote:
>
> On Tue, Apr 27, 2021 at 03:34:48PM +0800, kernel test robot wrote:
>>
>>
>> Greeting,
>>
>> FYI, we noticed a -2.3% regression of aim9.sync_disk_rw.ops_per_sec due to commit:
>
> Wow, that's very surprising, given that there are no pcpu allocations on any hot
> paths there.
>
> I tried hard to reproduce it, and I think I see something, however the data is
> very noisy. I'm not sure I can confidently attribute the regression to
> ace7e70901 ("percpu: use reclaim threshold instead of running for every page")
> rather than
> f183324133 ("percpu: implement partial chunk depopulation").
>
> Anyway, in my setup the following patch seems to fix the regression.
> Is it possible to test it?
>
> Thank you!
>
> Roman
>
> --
>
> From 6ee182110126cf93cf43389923bcf49ba12cb9a0 Mon Sep 17 00:00:00 2001
> From: Roman Gushchin <guro@...com>
> Date: Thu, 29 Apr 2021 18:01:40 -0700
> Subject: [PATCH] percpu: optimize locking in pcpu_balance_workfn()
>
> pcpu_balance_workfn() unconditionally calls pcpu_balance_free(),
> pcpu_reclaim_populated(), pcpu_balance_populated() and
> pcpu_balance_free() again.
>
> Each call to pcpu_balance_free() and pcpu_reclaim_populated() will
> cause at least one acquisition of the pcpu_lock. So even if the
> balancing was scheduled because of a failed atomic allocation,
> pcpu_lock will be acquired at least 4 times. This obviously
> increases the contention on the pcpu_lock.
>
> To optimize the scheme let's grab the pcpu_lock on the upper level
> (in pcpu_balance_workfn()) and keep it generally locked for the whole
> duration of the scheduled work, but release conditionally to perform
> any slow operations like chunk (de)population and creation of new chunks.
>
> Signed-off-by: Roman Gushchin <guro@...com>
> ---
> mm/percpu.c | 41 +++++++++++++++++++++++++++++------------
> 1 file changed, 29 insertions(+), 12 deletions(-)
>
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 245d89f6f0a9..f6bc8157cb3e 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -2005,6 +2005,9 @@ void __percpu *__alloc_reserved_percpu(size_t size, size_t align)
> * If empty_only is %false, reclaim all fully free chunks regardless of the
> * number of populated pages. Otherwise, only reclaim chunks that have no
> * populated pages.
> + *
> + * CONTEXT:
> + * pcpu_lock (can be dropped temporarily)
> */
> static void pcpu_balance_free(enum pcpu_chunk_type type, bool empty_only)
> {
> @@ -2013,12 +2016,12 @@ static void pcpu_balance_free(enum pcpu_chunk_type type, bool empty_only)
> struct list_head *free_head = &pcpu_slot[pcpu_free_slot];
> struct pcpu_chunk *chunk, *next;
>
> + lockdep_assert_held(&pcpu_lock);
> +
> /*
> * There's no reason to keep around multiple unused chunks and VM
> * areas can be scarce. Destroy all free chunks except for one.
> */
> - spin_lock_irq(&pcpu_lock);
> -
> list_for_each_entry_safe(chunk, next, free_head, list) {
> WARN_ON(chunk->immutable);
>
> @@ -2030,8 +2033,10 @@ static void pcpu_balance_free(enum pcpu_chunk_type type, bool empty_only)
> list_move(&chunk->list, &to_free);
> }
>
> - spin_unlock_irq(&pcpu_lock);
> + if (list_empty(&to_free))
> + return;
>
> + spin_unlock_irq(&pcpu_lock);
> list_for_each_entry_safe(chunk, next, &to_free, list) {
> unsigned int rs, re;
>
> @@ -2045,6 +2050,7 @@ static void pcpu_balance_free(enum pcpu_chunk_type type, bool empty_only)
> pcpu_destroy_chunk(chunk);
> cond_resched();
> }
> + spin_lock_irq(&pcpu_lock);
> }
>
> /**
> @@ -2056,6 +2062,9 @@ static void pcpu_balance_free(enum pcpu_chunk_type type, bool empty_only)
> * OOM killer to be triggered. We should avoid doing so until an actual
> * allocation causes the failure as it is possible that requests can be
> * serviced from already backed regions.
> + *
> + * CONTEXT:
> + * pcpu_lock (can be dropped temporarily)
> */
> static void pcpu_balance_populated(enum pcpu_chunk_type type)
> {
> @@ -2065,6 +2074,8 @@ static void pcpu_balance_populated(enum pcpu_chunk_type type)
> struct pcpu_chunk *chunk;
> int slot, nr_to_pop, ret;
>
> + lockdep_assert_held(&pcpu_lock);
> +
> /*
> * Ensure there are certain number of free populated pages for
> * atomic allocs. Fill up from the most packed so that atomic
> @@ -2092,13 +2103,11 @@ static void pcpu_balance_populated(enum pcpu_chunk_type type)
> if (!nr_to_pop)
> break;
>
> - spin_lock_irq(&pcpu_lock);
> list_for_each_entry(chunk, &pcpu_slot[slot], list) {
> nr_unpop = chunk->nr_pages - chunk->nr_populated;
> if (nr_unpop)
> break;
> }
> - spin_unlock_irq(&pcpu_lock);
>
> if (!nr_unpop)
> continue;
> @@ -2108,12 +2117,13 @@ static void pcpu_balance_populated(enum pcpu_chunk_type type)
> chunk->nr_pages) {
> int nr = min_t(int, re - rs, nr_to_pop);
>
> + spin_unlock_irq(&pcpu_lock);
> ret = pcpu_populate_chunk(chunk, rs, rs + nr, gfp);
> + cond_resched();
> + spin_lock_irq(&pcpu_lock);
> if (!ret) {
> nr_to_pop -= nr;
> - spin_lock_irq(&pcpu_lock);
> pcpu_chunk_populated(chunk, rs, rs + nr);
> - spin_unlock_irq(&pcpu_lock);
> } else {
> nr_to_pop = 0;
> }
> @@ -2125,11 +2135,12 @@ static void pcpu_balance_populated(enum pcpu_chunk_type type)
>
> if (nr_to_pop) {
> /* ran out of chunks to populate, create a new one and retry */
> + spin_unlock_irq(&pcpu_lock);
> chunk = pcpu_create_chunk(type, gfp);
> + cond_resched();
> + spin_lock_irq(&pcpu_lock);
> if (chunk) {
> - spin_lock_irq(&pcpu_lock);
> pcpu_chunk_relocate(chunk, -1);
> - spin_unlock_irq(&pcpu_lock);
> goto retry_pop;
> }
> }
> @@ -2146,6 +2157,10 @@ static void pcpu_balance_populated(enum pcpu_chunk_type type)
> * populated pages threshold, reintegrate the chunk if it has empty free pages.
> * Each chunk is scanned in the reverse order to keep populated pages close to
> * the beginning of the chunk.
> + *
> + * CONTEXT:
> + * pcpu_lock (can be dropped temporarily)
> + *
> */
> static void pcpu_reclaim_populated(enum pcpu_chunk_type type)
> {
> @@ -2155,7 +2170,7 @@ static void pcpu_reclaim_populated(enum pcpu_chunk_type type)
> LIST_HEAD(to_depopulate);
> int i, end;
>
> - spin_lock_irq(&pcpu_lock);
> + lockdep_assert_held(&pcpu_lock);
>
> list_splice_init(&pcpu_slot[pcpu_to_depopulate_slot], &to_depopulate);
>
> @@ -2231,8 +2246,6 @@ static void pcpu_reclaim_populated(enum pcpu_chunk_type type)
> &pcpu_slot[pcpu_to_depopulate_slot]);
> pcpu_schedule_balance_work();
> }
> -
> - spin_unlock_irq(&pcpu_lock);
> }
>
> /**
> @@ -2256,10 +2269,14 @@ static void pcpu_balance_workfn(struct work_struct *work)
> */
> for (type = 0; type < PCPU_NR_CHUNK_TYPES; type++) {
> mutex_lock(&pcpu_alloc_mutex);
> + spin_lock_irq(&pcpu_lock);
> +
> pcpu_balance_free(type, false);
> pcpu_reclaim_populated(type);
> pcpu_balance_populated(type);
> pcpu_balance_free(type, true);
> +
> + spin_unlock_irq(&pcpu_lock);
> mutex_unlock(&pcpu_alloc_mutex);
> }
> }
> --
> 2.30.2
Powered by blists - more mailing lists