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 9E2A5CA0EED for ; Thu, 21 Aug 2025 00:25:06 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E64CF8E000D; Wed, 20 Aug 2025 20:25:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E3C7D8E0008; Wed, 20 Aug 2025 20:25:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D79828E000D; Wed, 20 Aug 2025 20:25:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id C79988E0008 for ; Wed, 20 Aug 2025 20:25:05 -0400 (EDT) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 6B4A7B6D76 for ; Thu, 21 Aug 2025 00:25:05 +0000 (UTC) X-FDA: 83798869770.10.9CB0A5D Received: from out-180.mta0.migadu.com (out-180.mta0.migadu.com [91.218.175.180]) by imf07.hostedemail.com (Postfix) with ESMTP id 77E2E40003 for ; Thu, 21 Aug 2025 00:25:03 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=f1pzUfMI; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf07.hostedemail.com: domain of roman.gushchin@linux.dev designates 91.218.175.180 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1755735903; a=rsa-sha256; cv=none; b=tZ4cYCbX1O+OHRGXadD+AC9whqmROvYeY8wqQ0kYqWmVQOWoRWnm4eZ0qZqv8iUalMBikZ tmk2xI8LxVHGsfA7Jc6PWKgP3HcrUaFylwpbBrS4jY/9xvuWRqNrpqP6xsO3Lw11pNPQQU WbyQn9H7+NOr6j5lMo5p48Bq50iFYlk= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=f1pzUfMI; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf07.hostedemail.com: domain of roman.gushchin@linux.dev designates 91.218.175.180 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1755735903; 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=FX8HTbC4t5mzQ4enhPjum2fJkgBjClbezU/1uRSatWo=; b=sRcU6CKfH8wbbN1Bw+E+CQSgvrnx9VvxqgfDofbX7jx/fbRbZnxOmG7HA4/J5Pg5i3sbmA 0jRnnFpY3ctH+t+2ER7fa1RzJUVamXRJtTgjPqcnUj46rxpGKLKqHGcBdvpVQXlUsHGUfa AQa14pYom+pOBF1WnIBzREn/SfByEBU= 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=1755735901; 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=FX8HTbC4t5mzQ4enhPjum2fJkgBjClbezU/1uRSatWo=; b=f1pzUfMIl0HI3yotPn3qpxVBD1cKujg+g6E8HGFQ5nAimJQw+BiEoqriXFs4nxLNRKFJGL NPq2l0X93eWXYRqCBpbtt9pwXN7X3O1Nwr5+RPYx9X8y+cIS9ODDvrqbh70Sn6+Gq+RDFc HiORW6wg5SfKJnsYMAYau0YC1xkWHtE= 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 "Wed, 20 Aug 2025 13:28:46 +0200") References: <20250818170136.209169-1-roman.gushchin@linux.dev> <20250818170136.209169-2-roman.gushchin@linux.dev> Date: Wed, 20 Aug 2025 17:24:55 -0700 Message-ID: <87ms7tldwo.fsf@linux.dev> MIME-Version: 1.0 Content-Type: text/plain X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 77E2E40003 X-Stat-Signature: cc8po9dogboys1sgxpufcbpqk1c8gxsp X-HE-Tag: 1755735903-107000 X-HE-Meta: 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 TbDDMqMz /3ycJI7bZRImMN8/lAKHjGVzH1+tFa8a7paKbyL409iYfMxE3qRfeEQ1gq6SJlGS/ZbbJgX32lmZIKX02cc2xn2dpAOBe92yAepFWG2TsPnEUe+kWWo4Psq44wnAKZj7wb889gAgC9kwQMq2Gk3JC8OqoiNsVUjFrmsyDxJxJ9RNN0sf4RYIQhot7vfJnvHxZgx5SS0CyegnEdY8kHT+tHZFe9EQncHqyu+dFopap6FJPV4LUWnSWfdoyObjlXiVdGo5BoHYkN9Qd1hA= 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: 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. > How is it decided who gets to run before the other? Is it based on > order of attachment (which can be non-deterministic)? Yeah, now it's the order of attachment. > There was a lot of discussion on something similar for tc progs, and > we went with specific flags that capture partial ordering constraints > (instead of priorities that may collide). > https://lore.kernel.org/all/20230719140858.13224-2-daniel@iogearbox.net > It would be nice if we can find a way of making this consistent. I'll take a look, thanks! I hope that my naive approach might be good enough for the start and we can implement something more sophisticated later, but maybe I'm wrong here.