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[209.85.218.43]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a72ab065187sm441306066b.139.2024.07.02.10.28.21 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 Jul 2024 10:28:21 -0700 (PDT) Received: by mail-ej1-f43.google.com with SMTP id a640c23a62f3a-a72510ebc3fso667087066b.2 for ; Tue, 02 Jul 2024 10:28:21 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCW2jfXTYjIPre8nQeTF8bIE3o/mJPNrYiZqTOeE6APIKuAeYtOPJ1a/Fxl17UfB59Kg/NPyBS3RnlBX2snfw4nSiV0= X-Received: by 2002:a17:907:97d3:b0:a75:3c31:4f58 with SMTP id a640c23a62f3a-a753c315afdmr274936566b.32.1719941300909; Tue, 02 Jul 2024 10:28:20 -0700 (PDT) MIME-Version: 1.0 References: <202406270912.633e6c61-oliver.sang@intel.com> In-Reply-To: From: Linus Torvalds Date: Tue, 2 Jul 2024 10:28:04 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [linux-next:master] [lockref] d042dae6ad: unixbench.throughput -33.7% regression To: Mateusz Guzik Cc: Christian Brauner , kernel test robot , oe-lkp@lists.linux.dev, lkp@intel.com, Linux Memory Management List , linux-kernel@vger.kernel.org, ying.huang@intel.com, feng.tang@intel.com, fengwei.yin@intel.com Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 86C1340018 X-Stat-Signature: cf37rt98fjjzpbth1cku57zfq3rhzoah X-HE-Tag: 1719941303-457003 X-HE-Meta: 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 4+ov5wzr yfJL6K+XIcRPgwodXB35zmoQA6gQtzxrDx1Z+F6Loed8npBvwbEmGbqFDrfdoU8N3gzZLu/bbD5XHfdzY4HRqxcMYCAjfJsvzOf4vq0pxvFZj7mgwRzhwd1ot5ZFKJc1S5tFQtxq6NcuX4kZVV+lAcw0mDCCqxidE4E9ltjuDf4eU6q2V7Wpk8g6rgrkSsWNAtY4JebsTxYydY+VNOlPE9rcsgjQa++RynMBkinU+mcuSO7NEzJ3xUy9+Uwe7ee9yXg4V9ETmpL0ZIleC7R1jh9bPhxMTVSWIUoxPiRBMHP5YHVnUHKBrWZUtZwBp8o6Ft4yIds5l7eflIw1zV2TlPWVNm68hxdyOQ48lpG87pSffR5cLDIv7FUGHoKEG59ZcqvOO7jSuHlznyTGRmTLUz7gmFDSDSGdFjKhqMCeRqAK5Nql1n+uKxBBKLZv80MOYEMvJsNDgr+NDz615etxMGsfttncUWxKcjl07 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000009, 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 Tue, 2 Jul 2024 at 10:03, Mateusz Guzik wrote: > > I was thinking a different approach. > > A lookup variant which resolves everything and returns the dentry + an > information whether this is rcu mode. That would work equally. But the end result ends up being very similar: you need to hook into that final complete_walk() -> try_to_unlazy() -> legitimize_path() and check a flag whether you actually then do "get_lockref_or_dead()" or not. It really *shouldn't* be too bad, but this is just so subtle code that it just takes a lot of care. Even if the patch itself ends up not necessarily being very large. As mentioned, I've looked at it, but it always ended up being _just_ scary enough that I never really started doing it. Linus