From: Michal Hocko <mhocko@suse.com>
To: Ye Liu <ye.liu@linux.dev>
Cc: David Rientjes <rientjes@google.com>,
Shakeel Butt <shakeel.butt@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, Ye Liu <liuye@kylinos.cn>
Subject: Re: [PATCH] proc: Move OOM-related procfs code to fs/proc/oom.c
Date: Wed, 14 Oct 2026 11:32:11 +0200 [thread overview]
Message-ID: <as9MG_BtepLV6DsC@tiehlicka> (raw)
In-Reply-To: <20261014-oom_procfs-v1-1-f2d75e73571e@linux.dev>
On Wed 14-10-26 16:54:12, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
>
> fs/proc/base.c is a large file (~3700 lines) handling all per-process
> procfs entries. The OOM score, oom_adj, and oom_score_adj interface
> code is self-contained and has no dependencies on other parts of
> base.c, so move it into a dedicated fs/proc/oom.c following the same
> pattern as fs/proc/fd.c and fs/proc/task_mmu.c.
>
> This makes both files easier to read and keeps OOM-related procfs
> entries together in one place.
Are there plans to separate other functionality or is this one off
thing?
In general I am not against of moving stuff to more specialized files.
An obvious downside is a review as it is quite easy to overlook a subtle
change when moving so much code. Something worth undertaking if there
is a bigger goal. Not so sure if this is just a one of and fs/proc/base.c
still keeps other random stuff in.
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> ---
> MAINTAINERS | 1 +
> fs/proc/Makefile | 1 +
> fs/proc/base.c | 232 -------------------------------------------------
> fs/proc/internal.h | 8 ++
> fs/proc/oom.c | 249 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 5 files changed, 259 insertions(+), 232 deletions(-)
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 1da3623e77ce..4b1c13a65136 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -17676,6 +17676,7 @@ R: David Rientjes <rientjes@google.com>
> R: Shakeel Butt <shakeel.butt@linux.dev>
> L: linux-mm@kvack.org
> S: Maintained
> +F: fs/proc/oom.c
> F: include/linux/oom.h
> F: include/trace/events/oom.h
> F: include/uapi/linux/oom.h
> diff --git a/fs/proc/Makefile b/fs/proc/Makefile
> index 27e2b26b2d42..68e65866b5df 100644
> --- a/fs/proc/Makefile
> +++ b/fs/proc/Makefile
> @@ -21,6 +21,7 @@ proc-y += interrupts.o
> endif
> proc-y += loadavg.o
> proc-y += meminfo.o
> +proc-y += oom.o
> proc-y += stat.o
> proc-y += uptime.o
> proc-y += util.o
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 8c04fcd436d2..26ccc05a50ff 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -80,7 +80,6 @@
> #include <linux/audit.h>
> #include <linux/poll.h>
> #include <linux/nsproxy.h>
> -#include <linux/oom.h>
> #include <linux/elf.h>
> #include <linux/pid_namespace.h>
> #include <linux/user_namespace.h>
> @@ -99,7 +98,6 @@
> #include <linux/cn_proc.h>
> #include <linux/ksm.h>
> #include <uapi/linux/lsm.h>
> -#include <trace/events/oom.h>
> #include "internal.h"
> #include "fd.h"
>
> @@ -580,28 +578,6 @@ static const struct file_operations proc_lstats_operations = {
>
> #endif
>
> -static int proc_oom_score(struct seq_file *m, struct pid_namespace *ns,
> - struct pid *pid, struct task_struct *task)
> -{
> - unsigned long totalpages = totalram_pages() + total_swap_pages;
> - unsigned long points = 0;
> - long badness;
> -
> - badness = oom_badness(task, totalpages);
> - /*
> - * Special case OOM_SCORE_ADJ_MIN for all others scale the
> - * badness value into [0, 2000] range which we have been
> - * exporting for a long time so userspace might depend on it.
> - */
> - if (badness != LONG_MIN)
> - points = (OOM_SCORE_ADJ_MAX +
> - badness * OOM_SCORE_ADJ_MAX / (long)totalpages) * 2 / 3;
> -
> - seq_printf(m, "%lu\n", points);
> -
> - return 0;
> -}
> -
> struct limit_names {
> const char *name;
> const char *unit;
> @@ -1115,214 +1091,6 @@ static const struct file_operations proc_auxv_operations = {
> .release = mem_release,
> };
>
> -static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
> - loff_t *ppos)
> -{
> - struct task_struct *task = get_proc_task(file_inode(file));
> - char buffer[PROC_NUMBUF];
> - int oom_adj = OOM_ADJUST_MIN;
> - size_t len;
> -
> - if (!task)
> - return -ESRCH;
> - if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MAX)
> - oom_adj = OOM_ADJUST_MAX;
> - else
> - oom_adj = (task->signal->oom_score_adj * -OOM_DISABLE) /
> - OOM_SCORE_ADJ_MAX;
> - put_task_struct(task);
> - if (oom_adj > OOM_ADJUST_MAX)
> - oom_adj = OOM_ADJUST_MAX;
> - len = snprintf(buffer, sizeof(buffer), "%d\n", oom_adj);
> - return simple_read_from_buffer(buf, count, ppos, buffer, len);
> -}
> -
> -static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> -{
> - struct mm_struct *mm = NULL;
> - struct task_struct *task;
> - int err = 0;
> -
> - task = get_proc_task(file_inode(file));
> - if (!task)
> - return -ESRCH;
> -
> - mutex_lock(&oom_adj_mutex);
> - if (legacy) {
> - if (oom_adj < task->signal->oom_score_adj &&
> - !capable(CAP_SYS_RESOURCE)) {
> - err = -EACCES;
> - goto err_unlock;
> - }
> - /*
> - * /proc/pid/oom_adj is provided for legacy purposes, ask users to use
> - * /proc/pid/oom_score_adj instead.
> - */
> - pr_warn_once("%s (%d): /proc/%d/oom_adj is deprecated, please use /proc/%d/oom_score_adj instead.\n",
> - current->comm, task_pid_nr(current), task_pid_nr(task),
> - task_pid_nr(task));
> - } else {
> - if ((short)oom_adj < task->signal->oom_score_adj_min &&
> - !capable(CAP_SYS_RESOURCE)) {
> - err = -EACCES;
> - goto err_unlock;
> - }
> - }
> -
> - /*
> - * Make sure we will check other processes sharing the mm if this is
> - * not vfrok which wants its own oom_score_adj.
> - * pin the mm so it doesn't go away and get reused after task_unlock
> - */
> - if (!task->vfork_done) {
> - struct task_struct *p = find_lock_task_mm(task);
> -
> - if (p) {
> - if (mm_flags_test(MMF_MULTIPROCESS, p->mm)) {
> - mm = p->mm;
> - mmgrab(mm);
> - }
> - task_unlock(p);
> - }
> - }
> -
> - task->signal->oom_score_adj = oom_adj;
> - if (!legacy && has_capability_noaudit(current, CAP_SYS_RESOURCE))
> - task->signal->oom_score_adj_min = (short)oom_adj;
> - trace_oom_score_adj_update(task);
> -
> - if (mm) {
> - struct task_struct *p;
> -
> - rcu_read_lock();
> - for_each_process(p) {
> - if (same_thread_group(task, p))
> - continue;
> -
> - /* do not touch kernel threads or the global init */
> - if (p->flags & PF_KTHREAD || is_global_init(p))
> - continue;
> -
> - task_lock(p);
> - if (!p->vfork_done && process_shares_mm(p, mm)) {
> - p->signal->oom_score_adj = oom_adj;
> - if (!legacy && has_capability_noaudit(current, CAP_SYS_RESOURCE))
> - p->signal->oom_score_adj_min = (short)oom_adj;
> - }
> - task_unlock(p);
> - }
> - rcu_read_unlock();
> - mmdrop(mm);
> - }
> -err_unlock:
> - mutex_unlock(&oom_adj_mutex);
> - put_task_struct(task);
> - return err;
> -}
> -
> -/*
> - * /proc/pid/oom_adj exists solely for backwards compatibility with previous
> - * kernels. The effective policy is defined by oom_score_adj, which has a
> - * different scale: oom_adj grew exponentially and oom_score_adj grows linearly.
> - * Values written to oom_adj are simply mapped linearly to oom_score_adj.
> - * Processes that become oom disabled via oom_adj will still be oom disabled
> - * with this implementation.
> - *
> - * oom_adj cannot be removed since existing userspace binaries use it.
> - */
> -static ssize_t oom_adj_write(struct file *file, const char __user *buf,
> - size_t count, loff_t *ppos)
> -{
> - char buffer[PROC_NUMBUF] = {};
> - int oom_adj;
> - int err;
> -
> - if (count > sizeof(buffer) - 1)
> - count = sizeof(buffer) - 1;
> - if (copy_from_user(buffer, buf, count)) {
> - err = -EFAULT;
> - goto out;
> - }
> -
> - err = kstrtoint(strstrip(buffer), 0, &oom_adj);
> - if (err)
> - goto out;
> - if ((oom_adj < OOM_ADJUST_MIN || oom_adj > OOM_ADJUST_MAX) &&
> - oom_adj != OOM_DISABLE) {
> - err = -EINVAL;
> - goto out;
> - }
> -
> - /*
> - * Scale /proc/pid/oom_score_adj appropriately ensuring that a maximum
> - * value is always attainable.
> - */
> - if (oom_adj == OOM_ADJUST_MAX)
> - oom_adj = OOM_SCORE_ADJ_MAX;
> - else
> - oom_adj = (oom_adj * OOM_SCORE_ADJ_MAX) / -OOM_DISABLE;
> -
> - err = __set_oom_adj(file, oom_adj, true);
> -out:
> - return err < 0 ? err : count;
> -}
> -
> -static const struct file_operations proc_oom_adj_operations = {
> - .read = oom_adj_read,
> - .write = oom_adj_write,
> - .llseek = generic_file_llseek,
> -};
> -
> -static ssize_t oom_score_adj_read(struct file *file, char __user *buf,
> - size_t count, loff_t *ppos)
> -{
> - struct task_struct *task = get_proc_task(file_inode(file));
> - char buffer[PROC_NUMBUF];
> - short oom_score_adj = OOM_SCORE_ADJ_MIN;
> - size_t len;
> -
> - if (!task)
> - return -ESRCH;
> - oom_score_adj = task->signal->oom_score_adj;
> - put_task_struct(task);
> - len = snprintf(buffer, sizeof(buffer), "%hd\n", oom_score_adj);
> - return simple_read_from_buffer(buf, count, ppos, buffer, len);
> -}
> -
> -static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
> - size_t count, loff_t *ppos)
> -{
> - char buffer[PROC_NUMBUF] = {};
> - int oom_score_adj;
> - int err;
> -
> - if (count > sizeof(buffer) - 1)
> - count = sizeof(buffer) - 1;
> - if (copy_from_user(buffer, buf, count)) {
> - err = -EFAULT;
> - goto out;
> - }
> -
> - err = kstrtoint(strstrip(buffer), 0, &oom_score_adj);
> - if (err)
> - goto out;
> - if (oom_score_adj < OOM_SCORE_ADJ_MIN ||
> - oom_score_adj > OOM_SCORE_ADJ_MAX) {
> - err = -EINVAL;
> - goto out;
> - }
> -
> - err = __set_oom_adj(file, oom_score_adj, false);
> -out:
> - return err < 0 ? err : count;
> -}
> -
> -static const struct file_operations proc_oom_score_adj_operations = {
> - .read = oom_score_adj_read,
> - .write = oom_score_adj_write,
> - .llseek = default_llseek,
> -};
> -
> #ifdef CONFIG_AUDIT
> #define TMPBUFLEN 11
> static ssize_t proc_loginuid_read(struct file * file, char __user * buf,
> diff --git a/fs/proc/internal.h b/fs/proc/internal.h
> index df873df9afc5..b72a2bd604ed 100644
> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -238,6 +238,14 @@ static inline int folio_average_page_mapcount(struct folio *folio)
> /* ... but return at least 1. */
> return max_t(int, avg + entire_mapcount, 1);
> }
> +/*
> + * oom.c
> + */
> +int proc_oom_score(struct seq_file *m, struct pid_namespace *ns,
> + struct pid *pid, struct task_struct *task);
> +extern const struct file_operations proc_oom_adj_operations;
> +extern const struct file_operations proc_oom_score_adj_operations;
> +
> /*
> * array.c
> */
> diff --git a/fs/proc/oom.c b/fs/proc/oom.c
> new file mode 100644
> index 000000000000..5f22ec4a4a6e
> --- /dev/null
> +++ b/fs/proc/oom.c
> @@ -0,0 +1,249 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * OOM-related procfs entries
> + *
> + * This file handles the OOM score, oom_adj, and oom_score_adj interfaces
> + * in /proc/<pid>/.
> + */
> +
> +#include <linux/proc_fs.h>
> +#include <linux/oom.h>
> +#include <linux/seq_file.h>
> +#include <linux/capability.h>
> +#include <linux/mm.h>
> +#include <linux/swap.h>
> +#include <linux/sched/signal.h>
> +#include <linux/pid_namespace.h>
> +#include <trace/events/oom.h>
> +
> +#include "internal.h"
> +
> +int proc_oom_score(struct seq_file *m, struct pid_namespace *ns,
> + struct pid *pid, struct task_struct *task)
> +{
> + unsigned long totalpages = totalram_pages() + total_swap_pages;
> + unsigned long points = 0;
> + long badness;
> +
> + badness = oom_badness(task, totalpages);
> + /*
> + * Special case OOM_SCORE_ADJ_MIN for all others scale the
> + * badness value into [0, 2000] range which we have been
> + * exporting for a long time so userspace might depend on it.
> + */
> + if (badness != LONG_MIN)
> + points = (OOM_SCORE_ADJ_MAX +
> + badness * OOM_SCORE_ADJ_MAX / (long)totalpages) * 2 / 3;
> +
> + seq_printf(m, "%lu\n", points);
> +
> + return 0;
> +}
> +
> +static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
> + loff_t *ppos)
> +{
> + struct task_struct *task = get_proc_task(file_inode(file));
> + char buffer[PROC_NUMBUF];
> + int oom_adj = OOM_ADJUST_MIN;
> + size_t len;
> +
> + if (!task)
> + return -ESRCH;
> + if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MAX)
> + oom_adj = OOM_ADJUST_MAX;
> + else
> + oom_adj = (task->signal->oom_score_adj * -OOM_DISABLE) /
> + OOM_SCORE_ADJ_MAX;
> + put_task_struct(task);
> + if (oom_adj > OOM_ADJUST_MAX)
> + oom_adj = OOM_ADJUST_MAX;
> + len = snprintf(buffer, sizeof(buffer), "%d\n", oom_adj);
> + return simple_read_from_buffer(buf, count, ppos, buffer, len);
> +}
> +
> +static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> +{
> + struct mm_struct *mm = NULL;
> + struct task_struct *task;
> + int err = 0;
> +
> + task = get_proc_task(file_inode(file));
> + if (!task)
> + return -ESRCH;
> +
> + mutex_lock(&oom_adj_mutex);
> + if (legacy) {
> + if (oom_adj < task->signal->oom_score_adj &&
> + !capable(CAP_SYS_RESOURCE)) {
> + err = -EACCES;
> + goto err_unlock;
> + }
> + /*
> + * /proc/pid/oom_adj is provided for legacy purposes, ask users to use
> + * /proc/pid/oom_score_adj instead.
> + */
> + pr_warn_once("%s (%d): /proc/%d/oom_adj is deprecated, please use /proc/%d/oom_score_adj instead.\n",
> + current->comm, task_pid_nr(current), task_pid_nr(task),
> + task_pid_nr(task));
> + } else {
> + if ((short)oom_adj < task->signal->oom_score_adj_min &&
> + !capable(CAP_SYS_RESOURCE)) {
> + err = -EACCES;
> + goto err_unlock;
> + }
> + }
> +
> + /*
> + * Make sure we will check other processes sharing the mm if this is
> + * not vfrok which wants its own oom_score_adj.
> + * pin the mm so it doesn't go away and get reused after task_unlock
> + */
> + if (!task->vfork_done) {
> + struct task_struct *p = find_lock_task_mm(task);
> +
> + if (p) {
> + if (mm_flags_test(MMF_MULTIPROCESS, p->mm)) {
> + mm = p->mm;
> + mmgrab(mm);
> + }
> + task_unlock(p);
> + }
> + }
> +
> + task->signal->oom_score_adj = oom_adj;
> + if (!legacy && has_capability_noaudit(current, CAP_SYS_RESOURCE))
> + task->signal->oom_score_adj_min = (short)oom_adj;
> + trace_oom_score_adj_update(task);
> +
> + if (mm) {
> + struct task_struct *p;
> +
> + rcu_read_lock();
> + for_each_process(p) {
> + if (same_thread_group(task, p))
> + continue;
> +
> + /* do not touch kernel threads or the global init */
> + if (p->flags & PF_KTHREAD || is_global_init(p))
> + continue;
> +
> + task_lock(p);
> + if (!p->vfork_done && process_shares_mm(p, mm)) {
> + p->signal->oom_score_adj = oom_adj;
> + if (!legacy && has_capability_noaudit(current, CAP_SYS_RESOURCE))
> + p->signal->oom_score_adj_min = (short)oom_adj;
> + }
> + task_unlock(p);
> + }
> + rcu_read_unlock();
> + mmdrop(mm);
> + }
> +err_unlock:
> + mutex_unlock(&oom_adj_mutex);
> + put_task_struct(task);
> + return err;
> +}
> +
> +/*
> + * /proc/pid/oom_adj exists solely for backwards compatibility with previous
> + * kernels. The effective policy is defined by oom_score_adj, which has a
> + * different scale: oom_adj grew exponentially and oom_score_adj grows linearly.
> + * Values written to oom_adj are simply mapped linearly to oom_score_adj.
> + * Processes that become oom disabled via oom_adj will still be oom disabled
> + * with this implementation.
> + *
> + * oom_adj cannot be removed since existing userspace binaries use it.
> + */
> +static ssize_t oom_adj_write(struct file *file, const char __user *buf,
> + size_t count, loff_t *ppos)
> +{
> + char buffer[PROC_NUMBUF] = {};
> + int oom_adj;
> + int err;
> +
> + if (count > sizeof(buffer) - 1)
> + count = sizeof(buffer) - 1;
> + if (copy_from_user(buffer, buf, count)) {
> + err = -EFAULT;
> + goto out;
> + }
> +
> + err = kstrtoint(strstrip(buffer), 0, &oom_adj);
> + if (err)
> + goto out;
> + if ((oom_adj < OOM_ADJUST_MIN || oom_adj > OOM_ADJUST_MAX) &&
> + oom_adj != OOM_DISABLE) {
> + err = -EINVAL;
> + goto out;
> + }
> +
> + /*
> + * Scale /proc/pid/oom_score_adj appropriately ensuring that a maximum
> + * value is always attainable.
> + */
> + if (oom_adj == OOM_ADJUST_MAX)
> + oom_adj = OOM_SCORE_ADJ_MAX;
> + else
> + oom_adj = (oom_adj * OOM_SCORE_ADJ_MAX) / -OOM_DISABLE;
> +
> + err = __set_oom_adj(file, oom_adj, true);
> +out:
> + return err < 0 ? err : count;
> +}
> +
> +const struct file_operations proc_oom_adj_operations = {
> + .read = oom_adj_read,
> + .write = oom_adj_write,
> + .llseek = generic_file_llseek,
> +};
> +
> +static ssize_t oom_score_adj_read(struct file *file, char __user *buf,
> + size_t count, loff_t *ppos)
> +{
> + struct task_struct *task = get_proc_task(file_inode(file));
> + char buffer[PROC_NUMBUF];
> + short oom_score_adj = OOM_SCORE_ADJ_MIN;
> + size_t len;
> +
> + if (!task)
> + return -ESRCH;
> + oom_score_adj = task->signal->oom_score_adj;
> + put_task_struct(task);
> + len = snprintf(buffer, sizeof(buffer), "%hd\n", oom_score_adj);
> + return simple_read_from_buffer(buf, count, ppos, buffer, len);
> +}
> +
> +static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
> + size_t count, loff_t *ppos)
> +{
> + char buffer[PROC_NUMBUF] = {};
> + int oom_score_adj;
> + int err;
> +
> + if (count > sizeof(buffer) - 1)
> + count = sizeof(buffer) - 1;
> + if (copy_from_user(buffer, buf, count)) {
> + err = -EFAULT;
> + goto out;
> + }
> +
> + err = kstrtoint(strstrip(buffer), 0, &oom_score_adj);
> + if (err)
> + goto out;
> + if (oom_score_adj < OOM_SCORE_ADJ_MIN ||
> + oom_score_adj > OOM_SCORE_ADJ_MAX) {
> + err = -EINVAL;
> + goto out;
> + }
> +
> + err = __set_oom_adj(file, oom_score_adj, false);
> +out:
> + return err < 0 ? err : count;
> +}
> +
> +const struct file_operations proc_oom_score_adj_operations = {
> + .read = oom_score_adj_read,
> + .write = oom_score_adj_write,
> + .llseek = default_llseek,
> +};
>
> ---
> base-commit: 1fffefb00cc0b0da1f2ae24e3d33364530ea6515
> base-tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> change-id: 20261014-oom_procfs-f74a922f73f1
>
> Best regards,
> --
> Ye Liu <ye.liu@linux.dev>
--
Michal Hocko
SUSE Labs
prev parent reply other threads:[~2026-10-14 9:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-14 8:54 [PATCH] proc: Move OOM-related procfs code to fs/proc/oom.c Ye Liu
2026-10-14 9:32 ` Michal Hocko [this message]
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