From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (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 41B0B285CAA for ; Sat, 8 Aug 2026 14:08:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786198086; cv=none; b=YV/+8LosfDZLzsU+3VFCJsTgygiTCO9XtgsVHK2a7SD3jf4BwSNDSGQ8UtbeH9U5OYt0xhq9Nn0ZSNp12bgjE36u9VKTL4ZAkKiJ/eFAkbFC8Oss7EOsESwcZjZMb3fV5lZC486EPk1SwkE6HStiTlw7frGTsAuLlNXGNc5OaxA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786198086; c=relaxed/simple; bh=TmJrm89N6RG14n33SUAB/EiKXmPzuGvpEn78XOHy650=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=TFHqvCwHNKTjxIr6S0z6zm5L+LOk1SwUgAeIvbxg6OS3B5PUaTHe8cuc3tkqWBknc7RUUxx1Ce5rSHorzlr6fptck7x+MPPUAPbL1cERuG0ytcJ3wP8K5lH4CZIAqSFA2JtqUb4gLvJiWSev9ehHv09CpJPCKcNCTGR+pjsyG1c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=lqwYREcl; arc=none smtp.client-ip=91.218.175.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="lqwYREcl" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1786198071; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=jqYn1wblY9FldRcAfyRNPo2Ja5369GK00LFkYGT2PGI=; b=lqwYREclYrwGhxjyzbijgy59jiNCm0KT0p+38kjPZJfrt+pIWq+U7QcIZ46c/Tf0Vpzihj TmjcJT+o4jMv+cfb1KUjCU1PBb7dQOdWd4+7xOgjk+3TGTEaC4Jd+KFbedxI203JXvLfaG n+gqQp+mpp0KpXqk0EmOM5F46BC4+G8= From: Jiayuan Chen To: bpf@vger.kernel.org Cc: Jiayuan Chen , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , John Fastabend , Shuah Khan , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-rt-devel@lists.linux.dev Subject: [PATCH bpf-next v3 0/4] bpf: arena: handle memory.max on fault-in with reclaim/OOM Date: Sat, 8 Aug 2026 22:05:52 +0800 Message-ID: <20260808140720.293604-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Since commit e66fe1bc6d25 ("bpf: arena: Reintroduce memcg accounting"), arena pages are charged to the memcg of the process that created the arena. That accounting exposes two problems in the arena user page fault path. 1. The fault-in allocation runs under arena->spinlock, so it can only use the non-blocking allocator, which never reclaims. Once memory.current is at memory.max the allocation simply fails. Reaching memory.max is completely normal for a healthy application - e.g. reading a large file fills memory.current with page cache - so the process ends up killed for no real reason. 2. That failure is turned into VM_FAULT_SIGSEGV, which is misleading: the faulting address is a perfectly valid arena address. When we know it is an out-of-memory condition we can return VM_FAULT_OOM and let the memcg OOM path handle it properly. Preallocate the page outside the lock (patch 2), the way do_anonymous_page() does, so the allocation can sleep and go through reclaim and the OOM path. This needs a sleepable allocator (patch 1), because can_alloc_pages() is a conservative guess for BPF program context and always forces the non-blocking allocator under PREEMPT_RT. patch 3&4 adds a selftest that faults an arena in under a memory.max limit: without the fix the child gets SIGSEGV on a valid address, with it the child is killed by the memcg OOM killer. v2 -> v3: - selftest: check the memcg OOM via memory.events "oom_kill" instead of the exit signal; it only aims to pass on the fixed kernel, since the unfixed SIGSEGV is racy. v1 -> v2: - Rebase on the separate deadlock fix (found by the Sashiko AI review), now applied to bpf-next. - Honor the map's NUMA node on fault-in. - Return VM_FAULT_SIGBUS for the non-recoverable faults (lock, range-tree and page-table failures); a scratch-page hole stays VM_FAULT_SIGSEGV only under BPF_F_SEGV_ON_FAULT. (Kumar Kartikeya Dwivedi) - Add read_cgroup_file() to cgroup_helpers instead of open-coding the /mnt/... path in the test. (Emil Tsalapatis) - Dump the cgroup memory stats on test failure to ease debugging. v2: https://lore.kernel.org/bpf/20260805091720.139924-1-jiayuan.chen@linux.dev/ v1: https://lore.kernel.org/bpf/20260727062521.376231-1-jiayuan.chen@linux.dev/ Jiayuan Chen (4): bpf: Add a sleepable page allocator for map memory bpf: arena: allocate the fault-in page outside the lock selftests/bpf: Add read_cgroup_file() to cgroup_helpers selftests/bpf: Add a test for arena fault-in under memory.max include/linux/bpf.h | 1 + kernel/bpf/arena.c | 92 ++++++++--- kernel/bpf/syscall.c | 21 ++- tools/testing/selftests/bpf/cgroup_helpers.c | 67 ++++++++ tools/testing/selftests/bpf/cgroup_helpers.h | 4 + .../selftests/bpf/prog_tests/arena_memcg.c | 156 ++++++++++++++++++ .../testing/selftests/bpf/progs/arena_memcg.c | 24 +++ 7 files changed, 340 insertions(+), 25 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/arena_memcg.c create mode 100644 tools/testing/selftests/bpf/progs/arena_memcg.c -- 2.43.0