From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.31]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 718B55F861 for ; Thu, 1 Feb 2024 05:35:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=134.134.136.31 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706765712; cv=none; b=j/JskWllB1+OTCMb3y2SEChLAnSRVimN+4w7O/XzlpBHDcn/ob6id9/VmXJgW4PWw7fEsc0Q/zujrzNpS5WLHxVl73GN8hHiF4BNxiHuopp5G3GRCSHplypj9bw1VjAIpfg/km6CNjfLBTV95RGcm/2FcpASXqnUQIuQLjem+M0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706765712; c=relaxed/simple; bh=Ti8kVewtXtvIiMYx+XqzhxQNBkFEys/ij1bq33Pr8oE=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=GNN/HG68iorpg8MTGaFVB7iTLOvvR2kBDFX+D7eAlcYfDRStd11F24XaNUJpn4blPxMUMHt85XA3fcEO5jbw2IOa7dAn7QhF1rWatwcR/VijMd4AGHDWFY/6kN/ee5fOmWopzau5MSwNM+o2JJORt7wA5+/SCr+t8N7hsTg2LcI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=oA7DJfo7; arc=none smtp.client-ip=134.134.136.31 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="oA7DJfo7" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1706765710; x=1738301710; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version:content-transfer-encoding; bh=Ti8kVewtXtvIiMYx+XqzhxQNBkFEys/ij1bq33Pr8oE=; b=oA7DJfo7t4zmp7PFf/BEzefoAOaeLwss2NFJ0euuR3ujjKJNRM6al/xy TC2KRfWiR0qxWpY0qWupo9oOuH3aGNc3RBP/t3ylokKIvQ/6GZ3tj4kTR ru32JOIWVJd1+Qea8wM6TUMvqn0WYqs4YxeoMa283eT1yiBv6TbEaSOnQ 9rd4ItDQJMbXC23JwcXCGtiv+4hSKz3N1A3SB5b+rKsLpaf3A11O9Rl3i BCKLHfVS/s7J7x5XM6RppyYhF7KMvhp3hUUaxMrIw6TjCO56nw2sIrW0a 5eLQbfARzZubSjERiSODPNc9rtV9TtRp+phEwhONXBuZkdAUXEMgySEJU w==; X-IronPort-AV: E=McAfee;i="6600,9927,10969"; a="468049411" X-IronPort-AV: E=Sophos;i="6.05,234,1701158400"; d="scan'208";a="468049411" 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) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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,