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X-IronPort-AV: E=McAfee;i="6600,9927,10969"; a="468049413" X-IronPort-AV: E=Sophos;i="6.05,234,1701158400"; d="scan'208";a="468049413" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Jan 2024 21:35:09 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.05,234,1701158400"; d="scan'208";a="4313762" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Jan 2024 21:35:04 -0800 From: "Huang, Ying" To: Chris Li Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Wei =?utf-8?Q?Xu?= =?utf-8?Q?=EF=BF=BC?= , Yu =?utf-8?Q?Zhao=EF=BF=BC?= , Greg Thelen , Chun-Tse Shao , Suren =?utf-8?Q?Baghdasaryan=EF=BF=BC?= , Yosry =?utf-8?Q?A?= =?utf-8?Q?hmed=EF=BF=BC?= , Brain Geffon , Minchan Kim , Michal Hocko , Mel Gorman , Nhat Pham , Johannes Weiner , Kairui Song , Zhongkun He , Kemeng Shi , Barry Song Subject: Re: [PATCH v2] mm: swap: async free swap slot cache entries In-Reply-To: <20240131-async-free-v2-1-525f03e07184@kernel.org> (Chris Li's message of "Wed, 31 Jan 2024 17:17:31 -0800") References: <20240131-async-free-v2-1-525f03e07184@kernel.org> Date: Thu, 01 Feb 2024 13:33:07 +0800 Message-ID: <87sf2ceoks.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: uhr65793hud176xsfbbfcmj6ed9c66qf X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 175CB40017 X-Rspam-User: X-HE-Tag: 1706765711-545780 X-HE-Meta: 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 db0LuPGK 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Chris Li writes: > We discovered that 1% swap page fault is 100us+ while 50% of > the swap fault is under 20us. > > Further investigation show that a large portion of the time > spent in the free_swap_slots() function for the long tail case. > > The percpu cache of swap slots is freed in a batch of 64 entries > inside free_swap_slots(). These cache entries are accumulated > from previous page faults, which may not be related to the current > process. > > Doing the batch free in the page fault handler causes longer > tail latencies and penalizes the current process. > > Move free_swap_slots() outside of the swapin page fault handler into an > async work queue to avoid such long tail latencies. > > The batch free of swap slots is typically at 100us level. Such a Running ~100us operation in an asynchronous task appears overkill for me too. Can you try to move some operations out of swapcache_free_entries() to check whether that can resolve your issue? -- Best Regards, Huang, Ying > short time will not have a significant impact on the CPU accounting. > Notice that the previous swap slot batching behavior already performs > a delayed=C2=A0batch free. It=C2=A0waits for the entries=C2=A0accumulated= to 64. > Adding the async scheduling time does not change the original > free timing significantly. > > Testing: > > Chun-Tse did some benchmark in chromebook, showing that > zram_wait_metrics improve about 15% with 80% and 95% confidence. > > I recently ran some experiments on about 1000 Google production > machines. It shows swapin latency drops in the long tail > 100us - 500us bucket dramatically. > > platform (100-500us) (0-100us) > A 1.12% -> 0.36% 98.47% -> 99.22% > B 0.65% -> 0.15% 98.96% -> 99.46% > C 0.61% -> 0.23% 98.96% -> 99.38% > > Signed-off-by: Chris Li > To: Andrew Morton > Cc: linux-kernel@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: Wei Xu=EF=BF=BC > Cc: Yu Zhao=EF=BF=BC > Cc: Greg Thelen > Cc: Chun-Tse Shao > Cc: Suren Baghdasaryan=EF=BF=BC > Cc: Yosry Ahmed=EF=BF=BC > Cc: Brain Geffon > Cc: Minchan Kim > Cc: Michal Hocko > Cc: Mel Gorman > Cc: Huang Ying > Cc: Nhat Pham > Cc: Johannes Weiner > Cc: Kairui Song > Cc: Zhongkun He > Cc: Kemeng Shi > Cc: Barry Song > > remove create_work queue > > remove another work queue usage > > --- > Changes in v2: > - Add description of the impact of time changing suggest by Ying. > - Remove create_workqueue() and use schedule_work() > - Link to v1: https://lore.kernel.org/r/20231221-async-free-v1-1-94b27799= 2cb0@kernel.org > --- > include/linux/swap_slots.h | 1 + > mm/swap_slots.c | 29 +++++++++++++++++++++-------- > 2 files changed, 22 insertions(+), 8 deletions(-) > > diff --git a/include/linux/swap_slots.h b/include/linux/swap_slots.h > index 15adfb8c813a..67bc8fa30d63 100644 > --- a/include/linux/swap_slots.h > +++ b/include/linux/swap_slots.h > @@ -19,6 +19,7 @@ struct swap_slots_cache { > spinlock_t free_lock; /* protects slots_ret, n_ret */ > swp_entry_t *slots_ret; > int n_ret; > + struct work_struct async_free; > }; >=20=20 > void disable_swap_slots_cache_lock(void); > diff --git a/mm/swap_slots.c b/mm/swap_slots.c > index 0bec1f705f8e..71d344564e55 100644 > --- a/mm/swap_slots.c > +++ b/mm/swap_slots.c > @@ -44,6 +44,7 @@ static DEFINE_MUTEX(swap_slots_cache_mutex); > static DEFINE_MUTEX(swap_slots_cache_enable_mutex); >=20=20 > static void __drain_swap_slots_cache(unsigned int type); > +static void swapcache_async_free_entries(struct work_struct *data); >=20=20 > #define use_swap_slot_cache (swap_slot_cache_active && swap_slot_cache_e= nabled) > #define SLOTS_CACHE 0x1 > @@ -149,6 +150,7 @@ static int alloc_swap_slot_cache(unsigned int cpu) > spin_lock_init(&cache->free_lock); > cache->lock_initialized =3D true; > } > + INIT_WORK(&cache->async_free, swapcache_async_free_entries); > cache->nr =3D 0; > cache->cur =3D 0; > cache->n_ret =3D 0; > @@ -269,6 +271,20 @@ static int refill_swap_slots_cache(struct swap_slots= _cache *cache) > return cache->nr; > } >=20=20 > +static void swapcache_async_free_entries(struct work_struct *data) > +{ > + struct swap_slots_cache *cache; > + > + cache =3D container_of(data, struct swap_slots_cache, async_free); > + spin_lock_irq(&cache->free_lock); > + /* Swap slots cache may be deactivated before acquiring lock */ > + if (cache->slots_ret) { > + swapcache_free_entries(cache->slots_ret, cache->n_ret); > + cache->n_ret =3D 0; > + } > + spin_unlock_irq(&cache->free_lock); > +} > + > void free_swap_slot(swp_entry_t entry) > { > struct swap_slots_cache *cache; > @@ -282,17 +298,14 @@ void free_swap_slot(swp_entry_t entry) > goto direct_free; > } > if (cache->n_ret >=3D SWAP_SLOTS_CACHE_SIZE) { > - /* > - * Return slots to global pool. > - * The current swap_map value is SWAP_HAS_CACHE. > - * Set it to 0 to indicate it is available for > - * allocation in global pool > - */ > - swapcache_free_entries(cache->slots_ret, cache->n_ret); > - cache->n_ret =3D 0; > + spin_unlock_irq(&cache->free_lock); > + schedule_work(&cache->async_free); > + goto direct_free; > } > cache->slots_ret[cache->n_ret++] =3D entry; > spin_unlock_irq(&cache->free_lock); > + if (cache->n_ret >=3D SWAP_SLOTS_CACHE_SIZE) > + schedule_work(&cache->async_free); > } else { > direct_free: > swapcache_free_entries(&entry, 1); > > --- > base-commit: eacce8189e28717da6f44ee492b7404c636ae0de > change-id: 20231216-async-free-bef392015432 > > Best regards,