From patchwork Fri Sep 6 05:12:04 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrii Nakryiko X-Patchwork-Id: 13793240 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5C5AF54FB5; Fri, 6 Sep 2024 05:12:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725599539; cv=none; b=XN0DUKbVGOk6mGo26dM+M++1+dVgemaAbhDJRaZEUaV01GyM9msEDbLzCLeY3WI6CCiNd68IW2TSitc3tAX/SEaORRTzyG6C3UxaLvZYPUP9qFnwlNjiLf52uojsvZC24Tf1lvTiMI2FmE7MNY+P/v46yQZNmLFSEzksk1x5kDI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725599539; c=relaxed/simple; bh=QeJaV7NxUMr6y7gsUb56bD7q6rDPJGAUdKl0q2s8gUQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FhQ4U5cqN+n0ZZse0r3iEr89Nomv04bWA1IpfI23zJ6yH1vLI4K9RKmtr9+d1SWxFerj/QF1eBynWm1hQ5H8nZh1hAbIHO9lQ8zzJPfw3tpc7+ZcW6Gx19MMXSahX+h63tyIPP0G5fbuKOadVu0g1WHH6tCmtPiReo30bKZi5kk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rm0jdEna; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rm0jdEna" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B0516C4CEC8; Fri, 6 Sep 2024 05:12:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1725599538; bh=QeJaV7NxUMr6y7gsUb56bD7q6rDPJGAUdKl0q2s8gUQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rm0jdEnaH3gzrt/ZrzjYJggbJMRhkZ7pVttHT3Y+qQm8rP4KhY2QvSm9MAX8Eu2SE YsrL50oF9CAIz7Br9LxTh4dZT2uhC5roEACDiBZCrIoYMIk+yu7hwLc7AMIH6tFJar GRZ5BwFmqxuwpF6m6qRASY8wfKRHZWJ34QrPHK9cXo3OaHBwJ0urPXPHV4kJACdIBk Nz4szuc7WQA06iXoQBWbbcDWFJm9KnewfJ9cZ1gjWlI0NI+Pif3ioOEsAYa6s1uUy8 nUY5EWljCzZOS9t4CHvTPUDuvvpwtC30A8kEFcc5R3xvBR5SQ3jEUbBfkJYGlwt+MN fwoGEE4m1GKIQ== From: Andrii Nakryiko To: linux-trace-kernel@vger.kernel.org, peterz@infradead.org, oleg@redhat.com Cc: rostedt@goodmis.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, jolsa@kernel.org, paulmck@kernel.org, willy@infradead.org, surenb@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, mjguzik@gmail.com, brauner@kernel.org, jannh@google.com, Andrii Nakryiko Subject: [PATCH 1/2] mm: introduce mmap_lock_speculation_{start|end} Date: Thu, 5 Sep 2024 22:12:04 -0700 Message-ID: <20240906051205.530219-2-andrii@kernel.org> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20240906051205.530219-1-andrii@kernel.org> References: <20240906051205.530219-1-andrii@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Suren Baghdasaryan Add helper functions to speculatively perform operations without read-locking mmap_lock, expecting that mmap_lock will not be write-locked and mm is not modified from under us. A few will-it-scale ([0]) bechmarks were run with and without the changes in this patch on a beefy server. The test script below was used. Most of background activity on the server was stopped, but there could still be some sporadic sources of noise. And frankly, will-it-scale benchmarks themselves aren't 100% noise-free and do fluctuate somewhat. Also malloc1 benchmark was getting stuck for some reason, so it was skipped from benchmarks. But I think it was still useful as a bit of sanity check, but take all of them with a grain of salt. Benchmark script: # cat will_it_scale.sh #!/bin/bash set -eufo pipefail for b in page_fault1 page_fault2 page_fault3 malloc2; do for p in 40; do echo BENCH $b CPU$p $(will-it-scale/${b}_threads -m -t$p -s60 | grep average) done; done; Before (w/o this patch) ======================= BENCH page_fault1 CPU40 average:5403940 BENCH page_fault2 CPU40 average:5019159 BENCH page_fault3 CPU40 average:971057 BENCH malloc2 CPU40 average:1364730680 After (w/ this patch) ===================== BENCH page_fault1 CPU40 average:5485892 BENCH page_fault2 CPU40 average:5047923 BENCH page_fault3 CPU40 average:982953 BENCH malloc2 CPU40 average:1361339890 Results seem to be within the noise of measurements, but perhaps mm folks might have better benchmarks to try. [0] https://github.com/antonblanchard/will-it-scale Suggested-by: Peter Zijlstra Signed-off-by: Suren Baghdasaryan Signed-off-by: Andrii Nakryiko --- include/linux/mm_types.h | 3 +++ include/linux/mmap_lock.h | 53 +++++++++++++++++++++++++++++++-------- kernel/fork.c | 3 --- 3 files changed, 46 insertions(+), 13 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 485424979254..d5e3f907eea4 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -876,6 +876,9 @@ struct mm_struct { * Roughly speaking, incrementing the sequence number is * equivalent to releasing locks on VMAs; reading the sequence * number can be part of taking a read lock on a VMA. + * Incremented every time mmap_lock is write-locked/unlocked. + * Initialized to 0, therefore odd values indicate mmap_lock + * is write-locked and even values that it's released. * * Can be modified under write mmap_lock using RELEASE * semantics. diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index de9dc20b01ba..5410ce741d75 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -71,15 +71,12 @@ static inline void mmap_assert_write_locked(const struct mm_struct *mm) } #ifdef CONFIG_PER_VMA_LOCK -/* - * Drop all currently-held per-VMA locks. - * This is called from the mmap_lock implementation directly before releasing - * a write-locked mmap_lock (or downgrading it to read-locked). - * This should normally NOT be called manually from other places. - * If you want to call this manually anyway, keep in mind that this will release - * *all* VMA write locks, including ones from further up the stack. - */ -static inline void vma_end_write_all(struct mm_struct *mm) +static inline void init_mm_lock_seq(struct mm_struct *mm) +{ + mm->mm_lock_seq = 0; +} + +static inline void inc_mm_lock_seq(struct mm_struct *mm) { mmap_assert_write_locked(mm); /* @@ -91,19 +88,52 @@ static inline void vma_end_write_all(struct mm_struct *mm) */ smp_store_release(&mm->mm_lock_seq, mm->mm_lock_seq + 1); } + +static inline bool mmap_lock_speculation_start(struct mm_struct *mm, int *seq) +{ + /* Pairs with RELEASE semantics in inc_mm_lock_seq(). */ + *seq = smp_load_acquire(&mm->mm_lock_seq); + /* Allow speculation if mmap_lock is not write-locked */ + return (*seq & 1) == 0; +} + +static inline bool mmap_lock_speculation_end(struct mm_struct *mm, int seq) +{ + /* Pairs with RELEASE semantics in inc_mm_lock_seq(). */ + return seq == smp_load_acquire(&mm->mm_lock_seq); +} + #else -static inline void vma_end_write_all(struct mm_struct *mm) {} +static inline void init_mm_lock_seq(struct mm_struct *mm) {} +static inline void inc_mm_lock_seq(struct mm_struct *mm) {} +static inline bool mmap_lock_speculation_start(struct mm_struct *mm, int *seq) { return false; } +static inline bool mmap_lock_speculation_end(struct mm_struct *mm, int seq) { return false; } #endif +/* + * Drop all currently-held per-VMA locks. + * This is called from the mmap_lock implementation directly before releasing + * a write-locked mmap_lock (or downgrading it to read-locked). + * This should normally NOT be called manually from other places. + * If you want to call this manually anyway, keep in mind that this will release + * *all* VMA write locks, including ones from further up the stack. + */ +static inline void vma_end_write_all(struct mm_struct *mm) +{ + inc_mm_lock_seq(mm); +} + static inline void mmap_init_lock(struct mm_struct *mm) { init_rwsem(&mm->mmap_lock); + init_mm_lock_seq(mm); } static inline void mmap_write_lock(struct mm_struct *mm) { __mmap_lock_trace_start_locking(mm, true); down_write(&mm->mmap_lock); + inc_mm_lock_seq(mm); __mmap_lock_trace_acquire_returned(mm, true, true); } @@ -111,6 +141,7 @@ static inline void mmap_write_lock_nested(struct mm_struct *mm, int subclass) { __mmap_lock_trace_start_locking(mm, true); down_write_nested(&mm->mmap_lock, subclass); + inc_mm_lock_seq(mm); __mmap_lock_trace_acquire_returned(mm, true, true); } @@ -120,6 +151,8 @@ static inline int mmap_write_lock_killable(struct mm_struct *mm) __mmap_lock_trace_start_locking(mm, true); ret = down_write_killable(&mm->mmap_lock); + if (!ret) + inc_mm_lock_seq(mm); __mmap_lock_trace_acquire_returned(mm, true, ret == 0); return ret; } diff --git a/kernel/fork.c b/kernel/fork.c index 18bdc87209d0..c44b71d354ee 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1259,9 +1259,6 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, seqcount_init(&mm->write_protect_seq); mmap_init_lock(mm); INIT_LIST_HEAD(&mm->mmlist); -#ifdef CONFIG_PER_VMA_LOCK - mm->mm_lock_seq = 0; -#endif mm_pgtables_bytes_init(mm); mm->map_count = 0; mm->locked_vm = 0;