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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1755633984; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=UXfIhm/hFIhEPYTHFHNiLCBG8N/RRSHXsj3ucUlrP30=; b=uNscfs2tWZgwPR5KJ9uACyOxYqyI8cYOMmrh33u61mgc5NcdRc3I6XMtikRHVeTicTXgsD 30tfDjZufvQ3Xk1VQn44lIJs9X0maP99QBY56ofonxLD2owBiLa9R4yk+Orn8AgqzwnVu5 B6jNS4DNc6Z7/7U6szfmYgngRRD4YwA= From: Roman Gushchin To: Suren Baghdasaryan Cc: linux-mm@kvack.org, bpf@vger.kernel.org, Johannes Weiner , Michal Hocko , David Rientjes , Matt Bobrowski , Song Liu , Kumar Kartikeya Dwivedi , 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: (Suren Baghdasaryan's message of "Mon, 18 Aug 2025 21:09:12 -0700") References: <20250818170136.209169-1-roman.gushchin@linux.dev> <20250818170136.209169-2-roman.gushchin@linux.dev> Date: Tue, 19 Aug 2025 13:06:06 -0700 Message-ID: <878qjf13gx.fsf@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 397A2A000F X-Stat-Signature: 6ypzfz1o4j3y54fa4nim5fhsjbkny6r8 X-Rspam-User: X-HE-Tag: 1755633989-433767 X-HE-Meta: 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 JhEN7NIU OBhQfgtu3k8EY6AwlrFo0VAxn0tHQwmE509bh4sbRh3oooNuJPwLEs0r44yEnGVhCn3OhWaItO1TKNfikgZPCma7I8QK6+0aJec1s/vNnhGc0MVXOctner4fGTHrzwKW1EtWhLrGzhuHRA0iM9Ac3NulTQVS3P15lPu1YdiWlabUtGtrWnuhG7/t+UILsBbWdAaCcoXZ6HxRKDrw7q/5bxOYrmCezKv3Q9GU5Ei29jFBffiA= 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: Suren Baghdasaryan writes: > On Mon, Aug 18, 2025 at 10:01=E2=80=AFAM 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=3D format. "default" is printed if bpf is not >> used or policy name is not specified. >> >> [ 112.696676] test_progs invoked oom-killer: gfp_mask=3D0xcc0(GFP_KERNE= L), order=3D0, oom_score_adj=3D0 >> oom_policy=3Dbpf_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), BI= OS 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. >> >> Signed-off-by: Roman Gushchin >> --- >> include/linux/bpf_oom.h | 49 +++++++++++++ >> include/linux/oom.h | 8 ++ >> mm/Makefile | 3 + >> mm/bpf_oom.c | 157 ++++++++++++++++++++++++++++++++++++++++ >> mm/oom_kill.c | 22 +++++- >> 5 files changed, 237 insertions(+), 2 deletions(-) >> create mode 100644 include/linux/bpf_oom.h >> create mode 100644 mm/bpf_oom.c >> >> diff --git a/include/linux/bpf_oom.h b/include/linux/bpf_oom.h >> new file mode 100644 >> index 000000000000..29cb5ea41d97 >> --- /dev/null >> +++ b/include/linux/bpf_oom.h >> @@ -0,0 +1,49 @@ >> +/* SPDX-License-Identifier: GPL-2.0+ */ >> + >> +#ifndef __BPF_OOM_H >> +#define __BPF_OOM_H >> + >> +struct bpf_oom; >> +struct oom_control; >> + >> +#define BPF_OOM_NAME_MAX_LEN 64 >> + >> +struct bpf_oom_ops { >> + /** >> + * @handle_out_of_memory: Out of memory bpf handler, called befo= re >> + * the in-kernel OOM killer. >> + * @oc: OOM control structure >> + * >> + * Should return 1 if some memory was freed up, otherwise >> + * the in-kernel OOM killer is invoked. >> + */ >> + int (*handle_out_of_memory)(struct oom_control *oc); >> + >> + /** >> + * @name: BPF OOM policy name >> + */ >> + char name[BPF_OOM_NAME_MAX_LEN]; > > Why should the name be a part of ops structure? IMO it's not an > attribute of the operations but rather of the oom handler which is > represented by bpf_oom here. The ops structure describes a user-defined oom policy. Currently it's just one handler and the policy name. Later additional handlers can be added, e.g. a handler to control the dmesg output. bpf_oom is an implementation detail: it's basically an extension to struct bpf_oom_ops which contains "private" fields required for the internal machinery. > >> + >> + /* Private */ >> + struct bpf_oom *bpf_oom; >> +}; >> + >> +#ifdef CONFIG_BPF_SYSCALL >> +/** >> + * @bpf_handle_oom: handle out of memory using bpf programs >> + * @oc: OOM control structure >> + * >> + * Returns true if a bpf oom program was executed, returned 1 >> + * and some memory was actually freed. > > The above comment is unclear, please clarify. Fixed, thanks. /** * @bpf_handle_oom: handle out of memory condition using bpf * @oc: OOM control structure * * Returns true if some memory was freed. */ bool bpf_handle_oom(struct oom_control *oc); > >> + */ >> +bool bpf_handle_oom(struct oom_control *oc); >> + >> +#else /* CONFIG_BPF_SYSCALL */ >> +static inline bool bpf_handle_oom(struct oom_control *oc) >> +{ >> + return false; >> +} >> + >> +#endif /* CONFIG_BPF_SYSCALL */ >> + >> +#endif /* __BPF_OOM_H */ >> diff --git a/include/linux/oom.h b/include/linux/oom.h >> index 1e0fc6931ce9..ef453309b7ea 100644 >> --- a/include/linux/oom.h >> +++ b/include/linux/oom.h >> @@ -51,6 +51,14 @@ struct oom_control { >> >> /* Used to print the constraint info. */ >> enum oom_constraint constraint; >> + >> +#ifdef CONFIG_BPF_SYSCALL >> + /* Used by the bpf oom implementation to mark the forward progre= ss */ >> + bool bpf_memory_freed; >> + >> + /* Policy name */ >> + const char *bpf_policy_name; >> +#endif >> }; >> >> extern struct mutex oom_lock; >> diff --git a/mm/Makefile b/mm/Makefile >> index 1a7a11d4933d..a714aba03759 100644 >> --- a/mm/Makefile >> +++ b/mm/Makefile >> @@ -105,6 +105,9 @@ obj-$(CONFIG_MEMCG) +=3D memcontrol.o vmpressure.o >> ifdef CONFIG_SWAP >> obj-$(CONFIG_MEMCG) +=3D swap_cgroup.o >> endif >> +ifdef CONFIG_BPF_SYSCALL >> +obj-y +=3D bpf_oom.o >> +endif >> obj-$(CONFIG_CGROUP_HUGETLB) +=3D hugetlb_cgroup.o >> obj-$(CONFIG_GUP_TEST) +=3D gup_test.o >> obj-$(CONFIG_DMAPOOL_TEST) +=3D dmapool_test.o >> diff --git a/mm/bpf_oom.c b/mm/bpf_oom.c >> new file mode 100644 >> index 000000000000..47633046819c >> --- /dev/null >> +++ b/mm/bpf_oom.c >> @@ -0,0 +1,157 @@ >> +// SPDX-License-Identifier: GPL-2.0-or-later >> +/* >> + * BPF-driven OOM killer customization >> + * >> + * Author: Roman Gushchin >> + */ >> + >> +#include >> +#include >> +#include >> +#include >> + >> +DEFINE_STATIC_SRCU(bpf_oom_srcu); >> +static DEFINE_SPINLOCK(bpf_oom_lock); >> +static LIST_HEAD(bpf_oom_handlers); >> + >> +struct bpf_oom { > > Perhaps bpf_oom_handler ? Then bpf_oom_ops->bpf_oom could be called > bpf_oom_ops->handler. I don't think it's a handler, it's more like a private part of bpf_oom_ops. Maybe bpf_oom_impl? Idk > > >> + struct bpf_oom_ops *ops; >> + struct list_head node; >> + struct srcu_struct srcu; >> +}; >> + >> +bool bpf_handle_oom(struct oom_control *oc) >> +{ >> + struct bpf_oom_ops *ops; >> + struct bpf_oom *bpf_oom; >> + int list_idx, idx, ret =3D 0; >> + >> + oc->bpf_memory_freed =3D false; >> + >> + list_idx =3D srcu_read_lock(&bpf_oom_srcu); >> + list_for_each_entry_srcu(bpf_oom, &bpf_oom_handlers, node, false= ) { >> + ops =3D READ_ONCE(bpf_oom->ops); >> + if (!ops || !ops->handle_out_of_memory) >> + continue; >> + idx =3D srcu_read_lock(&bpf_oom->srcu); >> + oc->bpf_policy_name =3D ops->name[0] ? &ops->name[0] : >> + "bpf_defined_policy"; >> + ret =3D ops->handle_out_of_memory(oc); >> + oc->bpf_policy_name =3D NULL; >> + srcu_read_unlock(&bpf_oom->srcu, idx); >> + >> + if (ret && oc->bpf_memory_freed) > > IIUC ret and oc->bpf_memory_freed seem to reflect the same state: > handler successfully freed some memory. Could you please clarify when > they differ? The idea here is to provide an additional safety measure: if the bpf program simple returns 1 without doing anything, the system won't deadlock. oc->bpf_memory_freed is set by the bpf_oom_kill_process() helper (and potentially some other helpers in the future, e.g. bpf_oom_rm_tmpfs_file()) and can't be modified by the bpf program directly.