From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 33C43C28B20 for ; Sun, 30 Mar 2025 20:42:59 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 27FB0280002; Sun, 30 Mar 2025 16:42:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 22DBE280001; Sun, 30 Mar 2025 16:42:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 11F1F280002; Sun, 30 Mar 2025 16:42:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id E45FE280001 for ; Sun, 30 Mar 2025 16:42:56 -0400 (EDT) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 6268A1216BD for ; Sun, 30 Mar 2025 20:42:57 +0000 (UTC) X-FDA: 83279391594.22.906B6B6 Received: from mail-ed1-f46.google.com (mail-ed1-f46.google.com [209.85.208.46]) by imf19.hostedemail.com (Postfix) with ESMTP id 2BCD11A0007 for ; Sun, 30 Mar 2025 20:42:54 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=RY4KsyLP; spf=pass (imf19.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.208.46 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1743367375; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Q9bbo4m0YKczHWopSRDS1sLs4WUH12+PaT6dXT6fcFw=; b=z5lIS5gVXSXGm/nOqAFl3vdsQPbJ/t2079dUHgII4e1pGv4fa8xgqX0CLci0UMOTNXYl1v e989ew6SF4MnJ2ggpPOvW2MIdSBYt1329piBCGR5j6aOi62VIfeywF37mbosIE5ja7hDCM sOy4B/umnNM8dp8icvkEMbom7ZW0XEk= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=RY4KsyLP; spf=pass (imf19.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.208.46 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1743367375; a=rsa-sha256; cv=none; b=LvG4q3ozUicHo9IB2DJiPi65GizPvDUGgirmNw32u16CP+zdDSMMfJuJ6PLHO/GFvXw7Rt XMDd6wCuymTw9f9aKVhTaDflCp7YK86MQ1A4uM+sbQ2c0i8tveM/lZnLHTxnW1IEGerByi UMu4tMi9oi7H5ea5aDrixJajmJ8wpn8= Received: by mail-ed1-f46.google.com with SMTP id 4fb4d7f45d1cf-5e6f4b3ebe5so7103520a12.0 for ; Sun, 30 Mar 2025 13:42:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; t=1743367373; x=1743972173; darn=kvack.org; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=Q9bbo4m0YKczHWopSRDS1sLs4WUH12+PaT6dXT6fcFw=; b=RY4KsyLPksbjQu6dcQ8aTE5k69P0EFJX+7afxbojJqRuO/6+0397j9m0Lu4f7uStpR fbHw3/SC/eCo+qtvSwL6ApbNoYsvY1u1wjJv9NNOGkv2NMqXkgMGObrzdVRJISvigGXu R+E5YHXSOejmLy1d627rp0QSnzecXQnoKHLtY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1743367373; x=1743972173; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=Q9bbo4m0YKczHWopSRDS1sLs4WUH12+PaT6dXT6fcFw=; b=ndewZoOMPwX//46n2M5qQ9g+CvX0blXtmzX88kP22vICpEPb/dcttGpPhaFnHyfCjR B66lUWjD6vOL6MSQET7JiprYnDu+3U45KRIXcMCx7Q+bYHImpTOoY4W7Cj2pO+cInFUy E2hnFHi9mREjPbKI/3XDy0sJlsgqOm2c9tcnSK31124t82a1lAyAx7ODM026XSgCI8Rx rjcngAi0jW14AXlv4JcWtVquTRu3Ym3ntA2WvEJSTJ+tfyK2Y4YvmtAIpYFrdyNL5xJ7 EJTuJTi81iCLTY4XP9GRMvQe5D4hFZSWC4PxD3oDut/ujYjANc4VTD5OZzRgrY/Vp3Dy 9hag== X-Forwarded-Encrypted: i=1; AJvYcCWkR0a6ThXQV/QgWFax09UvwZWgs3MmI7eJio0fJXyS447Lfg4L3TGoZehtL72xuOCrDY4wca1Kfg==@kvack.org X-Gm-Message-State: AOJu0YzprvxfS+kKM55K87qRMWe/oHGfIFPksjgALQy67k8JoKAiGHqU PaMqwA/fulfWh85rn5MVCnb50eGRbpF2TuqUjMeM5oM5BD8Czza+gTHnK/IAlcX9xcBebckP/Fd wryM= X-Gm-Gg: ASbGnctSlI5Q7EPaez4of6DCRMFNWps6TPSxp48kAlnqIzWirlz0P6r087+mzWtB+jR RYSeBf3kgaKihG+8SpihU+B0eFP8rYC4TQlXNkAysS1x6FGthE9tz5Z8rZoaoTI1ojI8yg+vGrr tB02uSHHU9JO5w9SUzwIixM7t7B9H2klLUPXDWC1GRTznE5LXcXnGj+GLb2a2QmZWxEv6rlM58A ntYL5ee+NsKAE6rmfLl7ZawaRZG+NqTZtivJ7uPpLy4oPjIo8qSqWEZ9O1N+fTPwbrYAaG4C4UX FSOB73AbAfCV4aBJLlmOYXDwAEr+sLwGMllU928PQBWAWM7s79H9SXSZQVOx8BN6Q+RkRooQw8s 81foYKT64+ODKZr5B3Wg= X-Google-Smtp-Source: AGHT+IGkN/XxfAUFvyTk1pElL640rRCCLEhm4qZmHUW9FNw+bwiib8YUMJPJb83KTbaDgCbSWVviuQ== X-Received: by 2002:a05:6402:274e:b0:5ed:764f:dd73 with SMTP id 4fb4d7f45d1cf-5edfdafb4damr5612070a12.20.1743367373460; Sun, 30 Mar 2025 13:42:53 -0700 (PDT) Received: from mail-ej1-f42.google.com (mail-ej1-f42.google.com. [209.85.218.42]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5edd5c52379sm3588718a12.8.2025.03.30.13.42.50 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 30 Mar 2025 13:42:52 -0700 (PDT) Received: by mail-ej1-f42.google.com with SMTP id a640c23a62f3a-ac2c663a3daso765364166b.2 for ; Sun, 30 Mar 2025 13:42:50 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCVhJgnI5CsJNso8ibsrjKlH+2vjFz398dpDbDDO/8JKZG7d4583qlEf0FxmzbL8ZuM4a2fxlP08WA==@kvack.org X-Received: by 2002:a17:906:d553:b0:abf:6264:a624 with SMTP id a640c23a62f3a-ac738a8ea3amr567488066b.32.1743367370064; Sun, 30 Mar 2025 13:42:50 -0700 (PDT) MIME-Version: 1.0 References: <20250327145159.99799-1-alexei.starovoitov@gmail.com> In-Reply-To: <20250327145159.99799-1-alexei.starovoitov@gmail.com> From: Linus Torvalds Date: Sun, 30 Mar 2025 13:42:33 -0700 X-Gmail-Original-Message-ID: X-Gm-Features: AQ5f1Jo5PmHauyYbc5x0xsHSrONdOA84_jiW0Ke6tVTWo1pXzyKY5d-PBNExuF0 Message-ID: Subject: Re: [GIT PULL] Introduce try_alloc_pages for 6.15 To: Alexei Starovoitov Cc: bpf@vger.kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org, akpm@linux-foundation.org, peterz@infradead.org, vbabka@suse.cz, bigeasy@linutronix.de, rostedt@goodmis.org, mhocko@suse.com, shakeel.butt@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 2BCD11A0007 X-Stat-Signature: bx3hhd8oyxpyshh7f657sunq95wmnz4p X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1743367374-222747 X-HE-Meta: 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 fZpBJUCj 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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, 27 Mar 2025 at 07:52, Alexei Starovoitov wrote: > > The pull includes work from Sebastian, Vlastimil and myself > with a lot of help from Michal and Shakeel. > This is a first step towards making kmalloc reentrant to get rid > of slab wrappers: bpf_mem_alloc, kretprobe's objpool, etc. > These patches make page allocator safe from any context. So I've pulled this too, since it looked generally fine. The one reaction I had is that when you basically change spin_lock_irqsave(&zone->lock, flags); into if (!spin_trylock_irqsave(&zone->lock, flags)) { if (unlikely(alloc_flags & ALLOC_TRYLOCK)) return NULL; spin_lock_irqsave(&zone->lock, flags); } we've seen bad cache behavior for this kind of pattern in other situations: if the "try" fails, the subsequent "do the lock for real" case now does the wrong thing, in that it will immediately try again even if it's almost certainly just going to fail - causing extra write cache accesses. So typically, in places that can see contention, it's better to either do (a) trylock followed by a slowpath that takes the fact that it was locked into account and does a read-only loop until it sees otherwise This is, for example, what the mutex code does with that __mutex_trylock() -> mutex_optimistic_spin() pattern, but our spinlocks end up doing similar things (ie "trylock" followed by "release irq and do the 'relax loop' thing). or (b) do the trylock and lock separately, ie if (unlikely(alloc_flags & ALLOC_TRYLOCK)) { if (!spin_trylock_irqsave(&zone->lock, flags)) return NULL; } else spin_lock_irqsave(&zone->lock, flags); so that you don't end up doing two cache accesses for ownership that can cause extra bouncing. I'm not sure this matters at all in the allocation path - contention may simply not be enough of an issue, and the trylock is purely about "unlikely NMI worries", but I do worry that you might have made the normal case slower. It's easily fixable later if it ends up being the case, so I don't worry too much about it, but I did want to mention it since going through the code made me react to it. Linus