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From: Yosry Ahmed To: "Sridhar, Kanchana P" Cc: Nhat Pham , lkp , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "hannes@cmpxchg.org" , "chengming.zhou@linux.dev" , "usamaarif642@gmail.com" , "ryan.roberts@arm.com" , "21cnbao@gmail.com" <21cnbao@gmail.com>, "ying.huang@linux.alibaba.com" , "akpm@linux-foundation.org" , "linux-crypto@vger.kernel.org" , "herbert@gondor.apana.org.au" , "davem@davemloft.net" , "clabbe@baylibre.com" , "ardb@kernel.org" , "ebiggers@google.com" , "surenb@google.com" , "Accardi, Kristen C" , "llvm@lists.linux.dev" , "oe-kbuild-all@lists.linux.dev" , "Feghali, Wajdi K" , "Gopal, Vinodh" Subject: Re: [PATCH v8 14/14] mm: zswap: Compress batching with request chaining in zswap_store() of large folios. Message-ID: References: <20250303084724.6490-15-kanchana.p.sridhar@intel.com> <202503031847.j1iReOtf-lkp@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: fcghfkuhoyympte8pz11u14ac86yixps X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: E377E1A0016 X-Rspam-User: X-HE-Tag: 1741296064-590555 X-HE-Meta: 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 M9A2ulsi 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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: On Mon, Mar 03, 2025 at 09:34:04PM +0000, Sridhar, Kanchana P wrote: > > > -----Original Message----- > > From: Nhat Pham > > Sent: Monday, March 3, 2025 10:22 AM > > To: lkp > > Cc: Sridhar, Kanchana P ; linux- > > kernel@vger.kernel.org; linux-mm@kvack.org; hannes@cmpxchg.org; > > yosry.ahmed@linux.dev; chengming.zhou@linux.dev; > > usamaarif642@gmail.com; ryan.roberts@arm.com; 21cnbao@gmail.com; > > ying.huang@linux.alibaba.com; akpm@linux-foundation.org; linux- > > crypto@vger.kernel.org; herbert@gondor.apana.org.au; > > davem@davemloft.net; clabbe@baylibre.com; ardb@kernel.org; > > ebiggers@google.com; surenb@google.com; Accardi, Kristen C > > ; llvm@lists.linux.dev; oe-kbuild- > > all@lists.linux.dev; Feghali, Wajdi K ; Gopal, > > Vinodh > > Subject: Re: [PATCH v8 14/14] mm: zswap: Compress batching with request > > chaining in zswap_store() of large folios. > > > > On Mon, Mar 3, 2025 at 3:07 AM kernel test robot wrote: > > > > > > Hi Kanchana, > > > > > > kernel test robot noticed the following build errors: > > > > > > > 1166 prefetchw(entries[j]); > > > -- > > > > Why are we doing this anyway? Does it have a notable performance > > difference? At the very least, leave a comment explaining why we're > > prefetching this (although the build error suggests that we have to > > remove it anyway). > > Hi Nhat, > > Yes, it does. The use of prefetchw reduces sys time by ~1.5% because > it minimizes cache-miss latency by moving the zswap entry to the cache > before it is written to. > > This is data with kernel compilation test, v8 without prefetchw and v8 as-is: > > -------------------------------------------------------------------------------- > Kernel compile v8 without v8 v8 without v8 > allmodconfig prefetchw prefetchw > 2M folios > -------------------------------------------------------------------------------- > zswap compressor deflate-iaa deflate-iaa zstd zstd > -------------------------------------------------------------------------------- > real_sec 732.89 735.63 768.53 758.21 > user_sec 15,708.37 15,699.84 15,702.64 15,678.73 > sys_sec 4,632.58 4,563.70 5,735.06 5,635.69 > -------------------------------------------------------------------------------- > Max_Res_Set_Size_KB 1,874,672 1,867,516 1,874,684 1,872,888 > -------------------------------------------------------------------------------- > memcg_high 0 0 0 0 > memcg_swap_fail 0 0 0 0 > zswpout 114,742,930 112,836,725 92,904,961 89,596,085 > zswpin 41,184,897 39,983,793 31,018,149 29,163,932 > pswpout 625 1,069 558 1,059 > pswpin 599 1,056 540 1,051 > thp_swpout 1 2 1 2 > thp_swpout_fallback 10,967 10,195 6,918 6,141 > pgmajfault 42,588,331 41,349,069 31,931,882 30,006,422 > ZSWPOUT-2048kB 7,661 8,710 6,799 7,480 > SWPOUT-2048kB 1 2 1 2 > -------------------------------------------------------------------------------- > > > Sure, I will add a comment, and also "#include " in zswap.c > that will resolve the build error. This is similar to how these files handle prefetchw: > mm/vmscan.c, kernel/locking/qspinlock.c, include/asm-generic/xor.h, etc. Please also explicitly mention that the prefetch and likely/unlikely annotations prevent regressions with software compression like zstd, and generally improve the performance with the batching code by ~1.5%. > > Thanks, > Kanchana >