From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D81FD76EEA for ; Tue, 12 Mar 2024 08:45:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710233128; cv=none; b=O3JDejSzg+c/2ZzuGU7k0klXLisowvLB4KJt1CclYIWlPAqGyUvp6v/UcXLdjLEFNSyU5MZOO70Yj/RS0dzAKfeMKM97YLJr9UfFnS4Ji8yUEF7UBxKQwT+wVV2gdGx78FSPBN/ZccaMA/VpDpp9+iAc9FGBhY6MpdXki9CocW0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710233128; c=relaxed/simple; bh=geOnI5+yro433FwcsqWEKQU6S+hcouaat93T1RGM1As=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eGcZiclhiOYfLZpmnbjacBAV5DBrMn21aLI+55E+f1F8nGbIPpCvQ4MkdFyPsTpf34ZMo1zNZauK3vt1MJGR0LUolKH6cxcvgfrPPbxbTRSTr7XU2NjdW3WXq+EqlvdY/S1oL8MS2HzNVokmcq6tDMz6d7ewG98GMMsTRy2BXIE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id ED2B11007; Tue, 12 Mar 2024 01:46:01 -0700 (PDT) Received: from [10.57.68.246] (unknown [10.57.68.246]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 81D7E3F73F; Tue, 12 Mar 2024 01:45:22 -0700 (PDT) Message-ID: Date: Tue, 12 Mar 2024 08:45:20 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 0/6] Swap-out mTHP without splitting Content-Language: en-GB To: Andrew Morton , David Hildenbrand , Matthew Wilcox , Huang Ying , Gao Xiang , Yu Zhao , Yang Shi , Michal Hocko , Kefeng Wang , Barry Song <21cnbao@gmail.com>, Chris Li Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240311150058.1122862-1-ryan.roberts@arm.com> From: Ryan Roberts In-Reply-To: <20240311150058.1122862-1-ryan.roberts@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/03/2024 15:00, Ryan Roberts wrote: > Hi All, > > This series adds support for swapping out multi-size THP (mTHP) without needing > to first split the large folio via split_huge_page_to_list_to_order(). It > closely follows the approach already used to swap-out PMD-sized THP. > > There are a couple of reasons for swapping out mTHP without splitting: > > - Performance: It is expensive to split a large folio and under extreme memory > pressure some workloads regressed performance when using 64K mTHP vs 4K > small folios because of this extra cost in the swap-out path. This series > not only eliminates the regression but makes it faster to swap out 64K mTHP > vs 4K small folios. > > - Memory fragmentation avoidance: If we can avoid splitting a large folio > memory is less likely to become fragmented, making it easier to re-allocate > a large folio in future. > > - Performance: Enables a separate series [4] to swap-in whole mTHPs, which > means we won't lose the TLB-efficiency benefits of mTHP once the memory has > been through a swap cycle. > > I've done what I thought was the smallest change possible, and as a result, this > approach is only employed when the swap is backed by a non-rotating block device > (just as PMD-sized THP is supported today). Discussion against the RFC concluded > that this is sufficient. > > > Performance Testing > =================== > > I've run some swap performance tests on Ampere Altra VM (arm64) with 8 CPUs. The > VM is set up with a 35G block ram device as the swap device and the test is run > from inside a memcg limited to 40G memory. I've then run `usemem` from > vm-scalability with 70 processes, each allocating and writing 1G of memory. I've > repeated everything 6 times and taken the mean performance improvement relative > to 4K page baseline: > > | alloc size | baseline | + this series | > | | v6.6-rc4+anonfolio | | Oops, just noticed I failed to update these column headers. The baseline is actually mm-unstable (d7182786dd0a) which is based on v6.8-rc5 and already contains "anonfolio" - now called mTHP. > |:-----------|--------------------:|--------------------:| > | 4K Page | 0.0% | 1.4% | > | 64K THP | -14.6% | 44.2% | > | 2M THP | 87.4% | 97.7% | > > So with this change, the 64K swap performance goes from a 15% regression to a > 44% improvement. 4K and 2M swap improves slightly too. > > This test also acts as a good stress test for swap and, more generally mm. A > couple of existing bugs were found as a result [5] [6]. > > > --- > The series applies against mm-unstable (d7182786dd0a). Although I've > additionally been running with a couple of extra fixes to avoid the issues at > [6]. > > > Changes since v3 [3] > ==================== > > - Renamed SWAP_NEXT_NULL -> SWAP_NEXT_INVALID (per Huang, Ying) > - Simplified max offset calculation (per Huang, Ying) > - Reinstated struct percpu_cluster to contain per-cluster, per-order `next` > offset (per Huang, Ying) > - Removed swap_alloc_large() and merged its functionality into > scan_swap_map_slots() (per Huang, Ying) > - Avoid extra cost of folio ref and lock due to removal of CLUSTER_FLAG_HUGE > by freeing swap entries in batches (see patch 2) (per DavidH) > - vmscan splits folio if its partially mapped (per Barry Song, DavidH) > - Avoid splitting in MADV_PAGEOUT path (per Barry Song) > - Dropped "mm: swap: Simplify ssd behavior when scanner steals entry" patch > since it's not actually a problem for THP as I first thought. > > > Changes since v2 [2] > ==================== > > - Reuse scan_swap_map_try_ssd_cluster() between order-0 and order > 0 > allocation. This required some refactoring to make everything work nicely > (new patches 2 and 3). > - Fix bug where nr_swap_pages would say there are pages available but the > scanner would not be able to allocate them because they were reserved for the > per-cpu allocator. We now allow stealing of order-0 entries from the high > order per-cpu clusters (in addition to exisiting stealing from order-0 > per-cpu clusters). > > > Changes since v1 [1] > ==================== > > - patch 1: > - Use cluster_set_count() instead of cluster_set_count_flag() in > swap_alloc_cluster() since we no longer have any flag to set. I was unable > to kill cluster_set_count_flag() as proposed against v1 as other call > sites depend explicitly setting flags to 0. > - patch 2: > - Moved large_next[] array into percpu_cluster to make it per-cpu > (recommended by Huang, Ying). > - large_next[] array is dynamically allocated because PMD_ORDER is not > compile-time constant for powerpc (fixes build error). > > > [1] https://lore.kernel.org/linux-mm/20231010142111.3997780-1-ryan.roberts@arm.com/ > [2] https://lore.kernel.org/linux-mm/20231017161302.2518826-1-ryan.roberts@arm.com/ > [3] https://lore.kernel.org/linux-mm/20231025144546.577640-1-ryan.roberts@arm.com/ > [4] https://lore.kernel.org/linux-mm/20240304081348.197341-1-21cnbao@gmail.com/ > [5] https://lore.kernel.org/linux-mm/20240311084426.447164-1-ying.huang@intel.com/ > [6] https://lore.kernel.org/linux-mm/79dad067-1d26-4867-8eb1-941277b9a77b@arm.com/ > > Thanks, > Ryan > > > Ryan Roberts (6): > mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags > mm: swap: free_swap_and_cache_nr() as batched free_swap_and_cache() > mm: swap: Simplify struct percpu_cluster > mm: swap: Allow storage of all mTHP orders > mm: vmscan: Avoid split during shrink_folio_list() > mm: madvise: Avoid split during MADV_PAGEOUT and MADV_COLD > > include/linux/pgtable.h | 28 ++++ > include/linux/swap.h | 33 +++-- > mm/huge_memory.c | 3 - > mm/internal.h | 48 +++++++ > mm/madvise.c | 101 ++++++++------ > mm/memory.c | 13 +- > mm/swapfile.c | 298 ++++++++++++++++++++++------------------ > mm/vmscan.c | 9 +- > 8 files changed, 332 insertions(+), 201 deletions(-) > > -- > 2.25.1 >