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[209.85.208.50]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ac2394ff3easm132321866b.77.2025.03.06.10.04.35 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Mar 2025 10:04:35 -0800 (PST) Received: by mail-ed1-f50.google.com with SMTP id 4fb4d7f45d1cf-5e56b229d60so4012179a12.0 for ; Thu, 06 Mar 2025 10:04:35 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCUd36C2MpQA0TJcRh50rcYQdMWH/2XCQEk24+BMoyv5IPGTwrpO260hzG/NtP4W6WUSkufJCNEMDQ==@kvack.org X-Received: by 2002:a17:907:61a2:b0:ac1:e08c:6ac8 with SMTP id a640c23a62f3a-ac24e8a57dcmr59352966b.2.1741284274683; Thu, 06 Mar 2025 10:04:34 -0800 (PST) MIME-Version: 1.0 References: <20250306113924.20004-1-kprateek.nayak@amd.com> <20250306113924.20004-4-kprateek.nayak@amd.com> <20250306123245.GE19868@redhat.com> <20250306124120.GF19868@redhat.com> <39574d99-51a2-4314-989e-6331ca7c0d75@amd.com> In-Reply-To: <39574d99-51a2-4314-989e-6331ca7c0d75@amd.com> From: Linus Torvalds Date: Thu, 6 Mar 2025 08:04:18 -1000 X-Gmail-Original-Message-ID: X-Gm-Features: AQ5f1JoHVwZMPlgVDTPqJEc90ra_MHfbaLp-G-nJPvd2lDeghC0Pw92_liw9JP4 Message-ID: Subject: Re: [RFC PATCH 3/3] treewide: pipe: Convert all references to pipe->{head,tail,max_usage,ring_size} to unsigned short To: K Prateek Nayak Cc: Oleg Nesterov , Rasmus Villemoes , Miklos Szeredi , Alexander Viro , Christian Brauner , Andrew Morton , Hugh Dickins , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Jan Kara , "Matthew Wilcox (Oracle)" , Mateusz Guzik , "Gautham R. Shenoy" , Neeraj.Upadhyay@amd.com, Ananth.narayan@amd.com, Swapnil Sapkal Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 684B0140008 X-Stat-Signature: dxyztagad8otw1ugrwbesk7u1zn6wc83 X-HE-Tag: 1741284279-973402 X-HE-Meta: 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 uEJbIrlK 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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 Thu, 6 Mar 2025 at 05:33, K Prateek Nayak wrote: > >> > >> I dunno... but if we do this, perhaps we should > >> s/unsigned int/pipe_index_t instead? > >> > >> At least this would be more grep friendly. > > Ack. I'll leave the typedef untouched and convert these to use > pipe_index_t. This was an experiment so see if anything breaks with u16 > conversion just to get more testing on that scenario. As Rasmus > mentioned, leaving the head and tail as u32 on 64bit will lead to > better code generation. Yes, I was going to say the same - please don't change to 'unsigned short'. Judicious use of 'pipe_index_t' may be a good idea, but as I fixed some issues Rasmus found, I was also looking at the generated code, and on at least x86 where 16-bit generates extra instructions and prefixes, it seems marginally better to treat the values as 32-bit, and then only do the compares in 16 bits. That only causes a few "movzwl" instructions (at load time), and then the occasional "cmpw" (empty check) and "movw" (store) etc. But I only did a very quick "let's look at a few cases of x86-64 also using a 16-bit pipe_index_t". So for testing purposes your patch looks fine, but not as something to apply. If anything, I think we should actively try to remove as many direct accesses to these pipe fields as humanly possible. As Oleg said, a lot of them should just be cleaned up to use the helpers we already have. Rasmus found a few cases of that already, like that FIONREAD case where it was just doing a lot of open-coding of things that shouldn't be open-coded. I've fixed the two cases he pointed at up as obvious bugs, but it would be good to see where else issues like this might lurk. Linus