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SubjectRe: [PATCH v6] mm/ksm: introduce ksm_force for each process
Date
Hello.

On úterý 10. května 2022 14:22:42 CEST cgel.zte@gmail.com wrote:
> From: xu xin <xu.xin16@zte.com.cn>
>
> To use KSM, we have to explicitly call madvise() in application code,
> which means installed apps on OS needs to be uninstall and source code
> needs to be modified. It is inconvenient.
>
> In order to change this situation, We add a new proc file ksm_force
> under /proc/<pid>/ to support turning on/off KSM scanning of a
> process's mm dynamically.
>
> If ksm_force is set to 1, force all anonymous and 'qualified' VMAs
> of this mm to be involved in KSM scanning without explicitly calling
> madvise to mark VMA as MADV_MERGEABLE. But It is effective only when
> the klob of /sys/kernel/mm/ksm/run is set as 1.
>
> If ksm_force is set to 0, cancel the feature of ksm_force of this
> process (fallback to the default state) and unmerge those merged pages
> belonging to VMAs which is not madvised as MADV_MERGEABLE of this process,
> but still leave MADV_MERGEABLE areas merged.

To my best knowledge, last time a forcible KSM was discussed (see threads [1], [2], [3] and probably others) it was concluded that a) procfs was a horrible interface for things like this one; and b) process_madvise() syscall was among the best suggested places to implement this (which would require a more tricky handling from userspace, but still).

So, what changed since that discussion?

P.S. For now I do it via dedicated syscall, but I'm not trying to upstream this approach.

[1] https://lore.kernel.org/lkml/2a66abd8-4103-f11b-06d1-07762667eee6@suse.cz/
[2] https://lore.kernel.org/all/20190515145151.GG16651@dhcp22.suse.cz/T/#u
[3] https://lore.kernel.org/lkml/20190516172452.GA2106@avx2/
[4] https://gitlab.com/post-factum/pf-kernel/-/commits/ksm-5.17/

> Signed-off-by: xu xin <xu.xin16@zte.com.cn>
> Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
> Reviewed-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
> Reviewed-by: wangyong <wang.yong12@zte.com.cn>
> Reviewed-by: Yunkai Zhang <zhang.yunkai@zte.com.cn>
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> ---
> v6:
> - modify the way of "return"
> - remove unnecessary words in Documentation/admin-guide/mm/ksm.rst
> - add additional notes to "set 0 to ksm_force" in Documentation/../ksm.rst
> and Documentation/../proc.rst
> v5:
> - fix typos in Documentation/filesystem/proc.rst
> v4:
> - fix typos in commit log
> - add interface descriptions under Documentation/
> v3:
> - fix compile error of mm/ksm.c
> v2:
> - fix a spelling error in commit log.
> - remove a redundant condition check in ksm_force_write().
> ---
> Documentation/admin-guide/mm/ksm.rst | 19 +++++-
> Documentation/filesystems/proc.rst | 17 +++++
> fs/proc/base.c | 93 ++++++++++++++++++++++++++++
> include/linux/mm_types.h | 9 +++
> mm/ksm.c | 32 +++++++++-
> 5 files changed, 167 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
> index b244f0202a03..8cabc2504005 100644
> --- a/Documentation/admin-guide/mm/ksm.rst
> +++ b/Documentation/admin-guide/mm/ksm.rst
> @@ -32,7 +32,7 @@ are swapped back in: ksmd must rediscover their identity and merge again).
> Controlling KSM with madvise
> ============================
>
> -KSM only operates on those areas of address space which an application
> +KSM can operates on those areas of address space which an application
> has advised to be likely candidates for merging, by using the madvise(2)
> system call::
>
> @@ -70,6 +70,23 @@ Applications should be considerate in their use of MADV_MERGEABLE,
> restricting its use to areas likely to benefit. KSM's scans may use a lot
> of processing power: some installations will disable KSM for that reason.
>
> +Controlling KSM with procfs
> +===========================
> +
> +KSM can also operate on anonymous areas of address space of those processes's
> +knob ``/proc/<pid>/ksm_force`` is on, even if app codes doesn't call madvise()
> +explicitly to advise specific areas as MADV_MERGEABLE.
> +
> +You can set ksm_force to 1 to force all anonymous and qualified VMAs of
> +this process to be involved in KSM scanning.
> + e.g. ``echo 1 > /proc/<pid>/ksm_force``
> +
> +You can also set ksm_force to 0 to cancel that force feature of this process
> +and unmerge those merged pages which belongs to those VMAs not marked as
> +MADV_MERGEABLE of this process. But that still leave those pages belonging to
> +VMAs marked as MADV_MERGEABLE merged (fallback to the default state).
> + e.g. ``echo 0 > /proc/<pid>/ksm_force``
> +
> .. _ksm_sysfs:
>
> KSM daemon sysfs interface
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 061744c436d9..8890b8b457a4 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -47,6 +47,7 @@ fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009
> 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
> 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
> 3.12 /proc/<pid>/arch_status - Task architecture specific information
> + 3.13 /proc/<pid>/ksm_force - Setting of mandatory involvement in KSM
>
> 4 Configuring procfs
> 4.1 Mount options
> @@ -2176,6 +2177,22 @@ AVX512_elapsed_ms
> the task is unlikely an AVX512 user, but depends on the workload and the
> scheduling scenario, it also could be a false negative mentioned above.
>
> +3.13 /proc/<pid>/ksm_force - Setting of mandatory involvement in KSM
> +-----------------------------------------------------------------------
> +When CONFIG_KSM is enabled, this file can be used to specify if this
> +process's anonymous memory can be involved in KSM scanning without app codes
> +explicitly calling madvise to mark memory address as MADV_MERGEABLE.
> +
> +If writing 1 to this file, the kernel will force all anonymous and qualified
> +memory to be involved in KSM scanning without explicitly calling madvise to
> +mark memory address as MADV_MERGEABLE. But that is effective only when the
> +klob of '/sys/kernel/mm/ksm/run' is set as 1.
> +
> +If writing 0 to this file, the mandatory KSM feature of this process's will
> +be cancelled and unmerge those merged pages which belongs to those areas not
> +marked as MADV_MERGEABLE of this process, but leave those pages belonging to
> +areas marked as MADV_MERGEABLE merged (fallback to the default state).
> +
> Chapter 4: Configuring procfs
> =============================
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 8dfa36a99c74..d60f7342f79e 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -96,6 +96,7 @@
> #include <linux/time_namespace.h>
> #include <linux/resctrl.h>
> #include <linux/cn_proc.h>
> +#include <linux/ksm.h>
> #include <trace/events/oom.h>
> #include "internal.h"
> #include "fd.h"
> @@ -3168,6 +3169,96 @@ static int proc_pid_ksm_merging_pages(struct seq_file *m, struct pid_namespace *
>
> return 0;
> }
> +
> +static ssize_t ksm_force_read(struct file *file, char __user *buf, size_t count,
> + loff_t *ppos)
> +{
> + struct task_struct *task;
> + struct mm_struct *mm;
> + char buffer[PROC_NUMBUF];
> + ssize_t len;
> + int ret;
> +
> + task = get_proc_task(file_inode(file));
> + if (!task)
> + return -ESRCH;
> +
> + mm = get_task_mm(task);
> + ret = 0;
> + if (mm) {
> + len = snprintf(buffer, sizeof(buffer), "%d\n", mm->ksm_force);
> + ret = simple_read_from_buffer(buf, count, ppos, buffer, len);
> + mmput(mm);
> + }
> +
> + return ret;
> +}
> +
> +static ssize_t ksm_force_write(struct file *file, const char __user *buf,
> + size_t count, loff_t *ppos)
> +{
> + struct task_struct *task;
> + struct mm_struct *mm;
> + char buffer[PROC_NUMBUF];
> + int force;
> + int err = 0;
> +
> + memset(buffer, 0, sizeof(buffer));
> + if (count > sizeof(buffer) - 1)
> + count = sizeof(buffer) - 1;
> + if (copy_from_user(buffer, buf, count))
> + return -EFAULT;
> +
> + err = kstrtoint(strstrip(buffer), 0, &force);
> + if (err)
> + return err;
> +
> + if (force != 0 && force != 1)
> + return -EINVAL;
> +
> + task = get_proc_task(file_inode(file));
> + if (!task)
> + return -ESRCH;
> +
> + mm = get_task_mm(task);
> + if (!mm)
> + goto out_put_task;
> +
> + if (mm->ksm_force != force) {
> + if (mmap_write_lock_killable(mm)) {
> + err = -EINTR;
> + goto out_mmput;
> + }
> +
> + if (force == 0)
> + mm->ksm_force = force;
> + else {
> + /*
> + * Force anonymous pages of this mm to be involved in KSM merging
> + * without explicitly calling madvise.
> + */
> + if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
> + err = __ksm_enter(mm);
> + if (!err)
> + mm->ksm_force = force;
> + }
> +
> + mmap_write_unlock(mm);
> + }
> +
> +out_mmput:
> + mmput(mm);
> +out_put_task:
> + put_task_struct(task);
> +
> + return err < 0 ? err : count;
> +}
> +
> +static const struct file_operations proc_pid_ksm_force_operations = {
> + .read = ksm_force_read,
> + .write = ksm_force_write,
> + .llseek = generic_file_llseek,
> +};
> #endif /* CONFIG_KSM */
>
> #ifdef CONFIG_STACKLEAK_METRICS
> @@ -3303,6 +3394,7 @@ static const struct pid_entry tgid_base_stuff[] = {
> #endif
> #ifdef CONFIG_KSM
> ONE("ksm_merging_pages", S_IRUSR, proc_pid_ksm_merging_pages),
> + REG("ksm_force", S_IRUSR|S_IWUSR, proc_pid_ksm_force_operations),
> #endif
> };
>
> @@ -3639,6 +3731,7 @@ static const struct pid_entry tid_base_stuff[] = {
> #endif
> #ifdef CONFIG_KSM
> ONE("ksm_merging_pages", S_IRUSR, proc_pid_ksm_merging_pages),
> + REG("ksm_force", S_IRUSR|S_IWUSR, proc_pid_ksm_force_operations),
> #endif
> };
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index b34ff2cdbc4f..1b1592c2f5cf 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -661,6 +661,15 @@ struct mm_struct {
> * merging.
> */
> unsigned long ksm_merging_pages;
> + /*
> + * If true, force anonymous pages of this mm to be involved in KSM
> + * merging without explicitly calling madvise. It is effctive only
> + * when the klob of '/sys/kernel/mm/ksm/run' is set as 1. If false,
> + * cancel the feature of ksm_force of this process and unmerge
> + * those merged pages which is not madvised as MERGEABLE of this
> + * process, but leave MERGEABLE areas merged.
> + */
> + bool ksm_force;
> #endif
> } __randomize_layout;
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 38360285497a..c9f672dcc72e 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -334,6 +334,34 @@ static void __init ksm_slab_free(void)
> mm_slot_cache = NULL;
> }
>
> +/* Check if vma is qualified for ksmd scanning */
> +static bool ksm_vma_check(struct vm_area_struct *vma)
> +{
> + unsigned long vm_flags = vma->vm_flags;
> +
> + if (!(vma->vm_flags & VM_MERGEABLE) && !(vma->vm_mm->ksm_force))
> + return false;
> +
> + if (vm_flags & (VM_SHARED | VM_MAYSHARE |
> + VM_PFNMAP | VM_IO | VM_DONTEXPAND |
> + VM_HUGETLB | VM_MIXEDMAP))
> + return false; /* just ignore this vma*/
> +
> + if (vma_is_dax(vma))
> + return false;
> +
> +#ifdef VM_SAO
> + if (vm_flags & VM_SAO)
> + return false;
> +#endif
> +#ifdef VM_SPARC_ADI
> + if (vm_flags & VM_SPARC_ADI)
> + return false;
> +#endif
> +
> + return true;
> +}
> +
> static __always_inline bool is_stable_node_chain(struct stable_node *chain)
> {
> return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
> @@ -523,7 +551,7 @@ static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
> if (ksm_test_exit(mm))
> return NULL;
> vma = vma_lookup(mm, addr);
> - if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
> + if (!vma || !ksm_vma_check(vma) || !vma->anon_vma)
> return NULL;
> return vma;
> }
> @@ -2297,7 +2325,7 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
> vma = find_vma(mm, ksm_scan.address);
>
> for (; vma; vma = vma->vm_next) {
> - if (!(vma->vm_flags & VM_MERGEABLE))
> + if (!ksm_vma_check(vma))
> continue;
> if (ksm_scan.address < vma->vm_start)
> ksm_scan.address = vma->vm_start;
>


--
Oleksandr Natalenko (post-factum)


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