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Wed, 20 Aug 2025 12:35:09 -0700 (PDT) MIME-Version: 1.0 References: <20250818170136.209169-1-roman.gushchin@linux.dev> <20250818170136.209169-2-roman.gushchin@linux.dev> <878qjf13gx.fsf@linux.dev> In-Reply-To: <878qjf13gx.fsf@linux.dev> From: Suren Baghdasaryan Date: Wed, 20 Aug 2025 12:34:56 -0700 X-Gm-Features: Ac12FXy0lLRyFMPJP_Lri92PhEXXz9hvWGFjTmk5AjGe4AK2YQX_GDPqa3zp-wA Message-ID: Subject: Re: [PATCH v1 01/14] mm: introduce bpf struct ops for OOM handling To: Roman Gushchin 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: czuy84zrqb9k9rtmpo16kp7kabt89dgc X-Rspam-User: X-Rspamd-Queue-Id: DE1E616000E X-Rspamd-Server: rspam01 X-HE-Tag: 1755718510-827899 X-HE-Meta: U2FsdGVkX19D7Z0zDf3vNcxeLZbHaflfGGYUzqlz1QyFvqgVVFT2X+5qTxsFDHD3pRsVBD+5mD59/8AWkGagAh1fHSAzQYjX102xk7cGNtQ0KKY0BdJoeOdG5x1WJLQxmhsHIXsBGXIdTgrXffc2aBSneyUSZjk8VsQWMEKJDldIC8EhDdu15iDSMn1Ymkt9psejRBlfkWBUM/J4zSZg7KlwrJysvbQXQAd9uR+iZQDq1t7yUQ25CsTPaM32O0ykmAwa4nAM10VOV1XqvWS3DY2KmDO/CHlo0rxiEqTrj28kzyu/71n+Do5agTntMY2i9o817epXgwr8ccc2N2YlqXUtODy+hsUr6Lco0qRyD1x9YPk2+v75UrYugc85bj1zS50FFUqICtZHcKIyn3Fk9wAHBrNnZOcBMniD+sHZR3xvxGaRCf/ynMZMfukG092xn+HKlw1i/JsKxOldhn1/MM9/fehYp5U/SS4AwbC1PkIn0jNUF5UGKkHme7dZMpaDUPTPLCGJOxBOdLgA/k1qKvtE43YzVHsMAObGsfigaOf2lnjduA3u3bUC1Vab7fmz0s439EYo9EvP8fbnBZ9oB+dsHsDQwKIy7dMCRTzNshkbCytLk7Oo+zVzuBFssPH4fb5jnYltixJWG6qKhlcv3cAms2a1CS11Jdy8J4miroLmXPzjHwRz388wbPtkcy8OSmGPxtBUPk09SGjCsE1auLXyIrCAn1bB/ZniRkvK15pevnfcvItM5kBEtlWXj+mzunxJqEYOPuChHwkRmE3CjlKgCo8aKdgFY29K13/7WsSNIU7ckhHUtjh0fFGgk9dGU8O5fCNJlZ2PAipYzJE8Izeda22+KzhubB6f2tWWGnvZEIVHPqjt0kqZmDCCW7m2Tg1W0p1ylVnlY6+55ErNV84nyL4SUjLMcvxYMC++Di9rDPioL5RJy80XS6886nPmMoL0iTrptJSqQbjqJYU vdGOzP3y rjhqYUwP/wbzmXUm1Ku1uFhJiubVJyNiUhr9OTg5uhfMxDRZ6Qc0UbEkW4dm6dlaw7gP9H086EVVOweSN/90bQXW2HUHGRFoWbsb3VSWRNK4D3M6U7bzeuFH1Xow92zZsLvsYnUiX9yW+AulQMGvI/vIrycgeaELmB1i2Dti2IETiVMvFAIeQDb34Fo3fRthD8vTvbs77SGapgyeKxPA17OTOWACC5Pl8KgGu 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: On Tue, Aug 19, 2025 at 1:06=E2=80=AFPM Roman Gushchin wrote: > > 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 polici= es. > >> > >> 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 no= t > >> used or policy name is not specified. > >> > >> [ 112.696676] test_progs invoked oom-killer: gfp_mask=3D0xcc0(GFP_KER= NEL), order=3D0, oom_score_adj=3D0 > >> oom_policy=3Dbpf_test_policy > >> [ 112.698160] CPU: 1 UID: 0 PID: 660 Comm: test_progs Not tainted 6.1= 6.0-00015-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/0x3= 13 > >> [ 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 be= fore > >> + * 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. Ok. I hope we can come up with some more descriptive naming but I can't think of something good ATM. > > > > >> + > >> + /* 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 prog= ress */ > >> + 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 Yeah, we need to come up with some nomenclature and name these structs accordingly. In my mind ops means a structure that contains only operations, so current naming does not sit well but maybe that's just me... > > > > > > >> + 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, fal= se) { > >> + 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. I see. Then maybe we use only oc->bpf_memory_freed and handle_out_of_memory() does not return anything?