From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta0.migadu.com (out-180.mta0.migadu.com [91.218.175.180]) (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 2CD1F23BD02 for ; Thu, 21 Aug 2025 02:22:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755742972; cv=none; b=GUfbAzHbgKYtxT4P8QqYoh/dRp+gInnl6V0G3oUXroR8mq0W7uQKptiFYPogucagRGUxkI/O4+hB829CL7yNOTN25TbfbHj8tO47tAeW8rsF0XMrbUg7fPGbiHfdsBWPZKsF7SZZ6ERd3FAMMZCLVTkuEgnCgtqZH4mIoJkF5VQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755742972; c=relaxed/simple; bh=oDwbBGmgxy3vUPvM7avZroGuhizSxxMXx+qwF7bBMrE=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=IrAjkceI8FoVmbbCbfqqwRZeoQKlqNj2EiPlxGSso9nRPNXicO7mYLmJJeNGokg8NeoviFV6kwIDuJ9DwQiKk5NC1ujoIryiw3QdsmACjcVVluILJ/Zttqit6ZLUFx6LtbkIAeDaKEvLF7o7tz4dM1E5FdU6wQRoh2Gl2LD8YAg= 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=Suk4niCs; arc=none smtp.client-ip=91.218.175.180 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="Suk4niCs" 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=1755742958; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=j74vLZJ/pDTvrOLGmgUzsjwHFqEGtuc7kqWVVBs93lA=; b=Suk4niCsZPDfF3AjH92kMN99VOBt3dRVWTsdffSM0hmqybDSR7M+H6BQe0sxIveGb+8V/9 /sTqh0mdQNBNFIDknWXs8LeU5Y/lKkrNYX65al5YV4UQEcL5OzfCbhfAdc537GMe/n8xXP p8s623IbZqPxrfdYYuAifSgkbamO820= From: Roman Gushchin To: Kumar Kartikeya Dwivedi Cc: linux-mm@kvack.org, bpf@vger.kernel.org, Suren Baghdasaryan , Johannes Weiner , Michal Hocko , David Rientjes , Matt Bobrowski , Song Liu , Alexei Starovoitov , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 01/14] mm: introduce bpf struct ops for OOM handling In-Reply-To: (Kumar Kartikeya Dwivedi's message of "Thu, 21 Aug 2025 02:36:49 +0200") References: <20250818170136.209169-1-roman.gushchin@linux.dev> <20250818170136.209169-2-roman.gushchin@linux.dev> <87ms7tldwo.fsf@linux.dev> Date: Wed, 20 Aug 2025 19:22:31 -0700 Message-ID: <875xehh0rc.fsf@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-Migadu-Flow: FLOW_OUT Kumar Kartikeya Dwivedi writes: > On Thu, 21 Aug 2025 at 02:25, Roman Gushchin wrote: >> >> Kumar Kartikeya Dwivedi writes: >> >> > On Mon, 18 Aug 2025 at 19:01, Roman Gushchin wrote: >> >> >> >> Introduce a bpf struct ops for implementing custom OOM handling policies. >> >> >> >> The struct ops provides the bpf_handle_out_of_memory() callback, >> >> which expected to return 1 if it was able to free some memory and 0 >> >> otherwise. >> >> >> >> In the latter case it's guaranteed that the in-kernel OOM killer will >> >> be invoked. Otherwise the kernel also checks the bpf_memory_freed >> >> field of the oom_control structure, which is expected to be set by >> >> kfuncs suitable for releasing memory. It's a safety mechanism which >> >> prevents a bpf program to claim forward progress without actually >> >> releasing memory. The callback program is sleepable to enable using >> >> iterators, e.g. cgroup iterators. >> >> >> >> The callback receives struct oom_control as an argument, so it can >> >> easily filter out OOM's it doesn't want to handle, e.g. global vs >> >> memcg OOM's. >> >> >> >> The callback is executed just before the kernel victim task selection >> >> algorithm, so all heuristics and sysctls like panic on oom, >> >> sysctl_oom_kill_allocating_task and sysctl_oom_kill_allocating_task >> >> are respected. >> >> >> >> The struct ops also has the name field, which allows to define a >> >> custom name for the implemented policy. It's printed in the OOM report >> >> in the oom_policy= format. "default" is printed if bpf is not >> >> used or policy name is not specified. >> >> >> >> [ 112.696676] test_progs invoked oom-killer: gfp_mask=0xcc0(GFP_KERNEL), order=0, oom_score_adj=0 >> >> oom_policy=bpf_test_policy >> >> [ 112.698160] CPU: 1 UID: 0 PID: 660 Comm: test_progs Not tainted 6.16.0-00015-gf09eb0d6badc #102 PREEMPT(full) >> >> [ 112.698165] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-5.fc42 04/01/2014 >> >> [ 112.698167] Call Trace: >> >> [ 112.698177] >> >> [ 112.698182] dump_stack_lvl+0x4d/0x70 >> >> [ 112.698192] dump_header+0x59/0x1c6 >> >> [ 112.698199] oom_kill_process.cold+0x8/0xef >> >> [ 112.698206] bpf_oom_kill_process+0x59/0xb0 >> >> [ 112.698216] bpf_prog_7ecad0f36a167fd7_test_out_of_memory+0x2be/0x313 >> >> [ 112.698229] bpf__bpf_oom_ops_handle_out_of_memory+0x47/0xaf >> >> [ 112.698236] ? srso_alias_return_thunk+0x5/0xfbef5 >> >> [ 112.698240] bpf_handle_oom+0x11a/0x1e0 >> >> [ 112.698250] out_of_memory+0xab/0x5c0 >> >> [ 112.698258] mem_cgroup_out_of_memory+0xbc/0x110 >> >> [ 112.698274] try_charge_memcg+0x4b5/0x7e0 >> >> [ 112.698288] charge_memcg+0x2f/0xc0 >> >> [ 112.698293] __mem_cgroup_charge+0x30/0xc0 >> >> [ 112.698299] do_anonymous_page+0x40f/0xa50 >> >> [ 112.698311] __handle_mm_fault+0xbba/0x1140 >> >> [ 112.698317] ? srso_alias_return_thunk+0x5/0xfbef5 >> >> [ 112.698335] handle_mm_fault+0xe6/0x370 >> >> [ 112.698343] do_user_addr_fault+0x211/0x6a0 >> >> [ 112.698354] exc_page_fault+0x75/0x1d0 >> >> [ 112.698363] asm_exc_page_fault+0x26/0x30 >> >> [ 112.698366] RIP: 0033:0x7fa97236db00 >> >> >> >> It's possible to load multiple bpf struct programs. In the case of >> >> oom, they will be executed one by one in the same order they been >> >> loaded until one of them returns 1 and bpf_memory_freed is set to 1 >> >> - an indication that the memory was freed. This allows to have >> >> multiple bpf programs to focus on different types of OOM's - e.g. >> >> one program can only handle memcg OOM's in one memory cgroup. >> >> But the filtering is done in bpf - so it's fully flexible. >> > >> > I think a natural question here is ordering. Is this ability to have >> > multiple OOM programs critical right now? >> >> Good question. Initially I had only supported a single bpf policy. >> But then I realized that likely people would want to have different >> policies handling different parts of the cgroup tree. >> E.g. a global policy and several policies handling OOMs only >> in some memory cgroups. >> So having just a single policy is likely a no go. > > If the ordering is more to facilitate scoping, would it then be better > to support attaching the policy to specific memcg/cgroup? Well, it has some advantages and disadvantages. First, it will require way more infrastructure on the memcg side. Second, the interface is not super clear: we don't want to have a struct ops per cgroup, I guess. And in many case a single policy for all memcgs is just fine, so asking the user to attach it to all memcgs is just adding a toil and creating all kinds of races. So I see your point, but I'm not yet convinced, to be honest. Thanks!