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[209.85.128.53]) by smtp.gmail.com with ESMTPSA id n26-20020a170906379a00b007308fab3eb7sm90778ejc.195.2022.08.11.14.52.43 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Aug 2022 14:52:44 -0700 (PDT) Received: by mail-wm1-f53.google.com with SMTP id d24-20020a1c7318000000b003a5c1bf4f27so1251523wmb.4 for ; Thu, 11 Aug 2022 14:52:43 -0700 (PDT) X-Received: by 2002:a1c:2582:0:b0:3a5:1453:ca55 with SMTP id l124-20020a1c2582000000b003a51453ca55mr6664785wml.68.1660254762906; Thu, 11 Aug 2022 14:52:42 -0700 (PDT) MIME-Version: 1.0 References: <20220811152446.281723-1-idryomov@gmail.com> <5d0b0367a5e28ec5b1f3b995c7792ff9a5cbcbd4.camel@kernel.org> <72a93a2c8910c3615bba7c093c66c18b1a6a2696.camel@kernel.org> In-Reply-To: From: Linus Torvalds Date: Thu, 11 Aug 2022 14:52:26 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [GIT PULL] Ceph updates for 5.20-rc1 To: Al Viro Cc: Jeff Layton , Ilya Dryomov , ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org, Matthew Wilcox Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-1.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 11, 2022 at 2:38 PM Al Viro wrote: > > Exporting the functionality? Sure, no problem. Uninlining that one... > I suspect that it's OK, but I'd like to see profiling data; it's not > as if it would be hard to return to having it inlined, obviously. The only case where I think it might matter is in __d_lookup(), and it's probably not measurable. Yes, __d_lookup() does matter, but it only matters once you've fallen out of RCU mode, and at that point the cost of the function call is likely in the noise. I don't particularly like how it's inside that dentry hash chain loop, but realistically by then we've already done a function call for the dentry lock spinlock, so that loop already has to deal with it. Again, __d_lookup_rcu() is the place where adding a function call would matter more, because that one really does show up on profiles regularly. And it so carefully tries to avoid function calls (but the DCACHE_OP_COMPARE case causes problems: at one time a few years ago I actually wanted to move the DCACHE_OP_COMPARE *out* of the loop entirely, because it's loop invariant and having that unlikely cause inside the loop still causes bad things for register allocation). So I think the uninlining is fine. If I had been really unhappy about it I would have undone the pull. It was more the "I was told there would be cake, but there was no cake" that annoyed me. Linus