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Message-ID: <CAMXpfWtCROG-CyJWR1qM4k12dpRhKY92g3Mn74nokV_V-U+-cg@mail.gmail.com>
Date: Tue, 14 Jan 2025 16:46:08 +0100
From: Mario Casquero <mcasquer@...hat.com>
To: xu.xin16@....com.cn
Cc: akpm@...ux-foundation.org, david@...hat.com, linux-kernel@...r.kernel.org,
wang.yaxin@....com.cn, linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
yang.yang29@....com.cn
Subject: Re: [PATCH v5] ksm: add ksm involvement information for each process
This patch has been successfully tested. After starting the KSM and
obtaining the PID of a process, e.g. qemu-kvm PID, now the new items
can be checked.
echo 1 > /sys/kernel/mm/ksm/run
pid=$(pgrep -f "qemu-kvm")
cat /proc/$pid/ksm_stat
ksm_rmap_items 70692
ksm_zero_pages 0
ksm_merging_pages 4211
ksm_process_profit 12723968
ksm_merge_any: no
ksm_mergeable: yes
Tested-by: Mario Casquero <mcasquer@...hat.com>
On Fri, Jan 10, 2025 at 10:52 AM <xu.xin16@....com.cn> wrote:
>
> From: xu xin <xu.xin16@....com.cn>
>
> In /proc/<pid>/ksm_stat, Add two extra ksm involvement items including
> KSM_mergeable and KSM_merge_any. It helps administrators to
> better know the system's KSM behavior at process level.
>
> ksm_merge_any: yes/no
> whether the process'mm is added by prctl() into the candidate list
> of KSM or not, and fully enabled at process level.
>
> ksm_mergeable: yes/no
> whether any VMAs of the process'mm are currently applicable to KSM.
>
> Purpose
> =======
> These two items are just to improve the observability of KSM at process
> level, so that users can know if a certain process has enable KSM.
>
> For example, if without these two items, when we look at
> /proc/<pid>/ksm_stat and there's no merging pages found, We are not sure
> whether it is because KSM was not enabled or because KSM did not
> successfully merge any pages.
>
> Althrough "mg" in /proc/<pid>/smaps indicate VM_MERGEABLE, it's opaque
> and not very obvious for non professionals.
>
> Signed-off-by: xu xin <xu.xin16@....com.cn>
> Cc: Wang Yaxin <wang.yaxin@....com.cn>
> ---
> Changelog v4 -> v5:
> 1. Update the documentation.
> 2. Correct a comment sentence and add purpose statment in commit message.
> ---
> Documentation/filesystems/proc.rst | 66 ++++++++++++++++++++++++++++++++++++++
> fs/proc/base.c | 11 +++++++
> include/linux/ksm.h | 1 +
> mm/ksm.c | 19 +++++++++++
> 4 files changed, 97 insertions(+)
>
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 6a882c57a7e7..916f83203de0 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -48,6 +48,7 @@ fixes/update part 1.1 Stefani Seibold <stefani@...bold.net> June 9 2009
> 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
> 3.12 /proc/<pid>/arch_status - Task architecture specific information
> 3.13 /proc/<pid>/fd - List of symlinks to open files
> + 3.14 /proc/<pid/ksm_stat - Information about the process' ksm status.
>
> 4 Configuring procfs
> 4.1 Mount options
> @@ -2232,6 +2233,71 @@ The number of open files for the process is stored in 'size' member
> of stat() output for /proc/<pid>/fd for fast access.
> -------------------------------------------------------
>
> +3.14 /proc/<pid/ksm_stat - Information about the process' ksm status
> +--------------------------------------------------------------------
> +When CONFIG_KSM is enabled, each process has this file which displays
> +the information of ksm merging status.
> +
> +Example
> +~~~~~~~
> +
> +::
> +
> + / # cat /proc/self/ksm_stat
> + ksm_rmap_items 0
> + ksm_zero_pages 0
> + ksm_merging_pages 0
> + ksm_process_profit 0
> + ksm_merge_any: no
> + ksm_mergeable: no
> +
> +Description
> +~~~~~~~~~~~
> +
> +ksm_rmap_items
> +^^^^^^^^^^^^^^
> +
> +The number of ksm_rmap_item structure in use. The structure of
> +ksm_rmap_item is to store the reverse mapping information for virtual
> +addresses. KSM will generate a ksm_rmap_item for each ksm-scanned page
> +of the process.
> +
> +ksm_zero_pages
> +^^^^^^^^^^^^^^
> +
> +When /sys/kernel/mm/ksm/use_zero_pages is enabled, it represent how many
> +empty pages are merged with kernel zero pages by KSM.
> +
> +ksm_merging_pages
> +^^^^^^^^^^^^^^^^^
> +
> +It represents how many pages of this process are involved in KSM merging
> +(not including ksm_zero_pages). It is the same with what
> +/proc/<pid>/ksm_merging_pages shows.
> +
> +ksm_process_profit
> +^^^^^^^^^^^^^^^^^^
> +
> +The profit that KSM brings (Saved bytes). KSM can save memory by merging
> +identical pages, but also can consume additional memory, because it needs
> +to generate a number of rmap_items to save each scanned page's brief rmap
> +information. Some of these pages may be merged, but some may not be abled
> +to be merged after being checked several times, which are unprofitable
> +memory consumed.
> +
> +ksm_merge_any
> +^^^^^^^^^^^^^
> +
> +It specifies whether the process'mm is added by prctl() into the candidate list
> +of KSM or not, and KSM scanning is fully enabled at process level.
> +
> +ksm_mergeable
> +^^^^^^^^^^^^^
> +
> +It specifies whether any VMAs of the process'mm are currently applicable to KSM.
> +
> +More information about KSM can be found at Documentation/admin-guide/mm/ksm.rst.
> +
>
> Chapter 4: Configuring procfs
> =============================
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 0edf14a9840e..a50b222a5917 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3269,6 +3269,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
> struct pid *pid, struct task_struct *task)
> {
> struct mm_struct *mm;
> + int ret = 0;
>
> mm = get_task_mm(task);
> if (mm) {
> @@ -3276,6 +3277,16 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
> seq_printf(m, "ksm_zero_pages %ld\n", mm_ksm_zero_pages(mm));
> seq_printf(m, "ksm_merging_pages %lu\n", mm->ksm_merging_pages);
> seq_printf(m, "ksm_process_profit %ld\n", ksm_process_profit(mm));
> + seq_printf(m, "ksm_merge_any: %s\n",
> + test_bit(MMF_VM_MERGE_ANY, &mm->flags) ? "yes" : "no");
> + ret = mmap_read_lock_killable(mm);
> + if (ret) {
> + mmput(mm);
> + return ret;
> + }
> + seq_printf(m, "ksm_mergeable: %s\n",
> + ksm_process_mergeable(mm) ? "yes" : "no");
> + mmap_read_unlock(mm);
> mmput(mm);
> }
>
> diff --git a/include/linux/ksm.h b/include/linux/ksm.h
> index 6a53ac4885bb..d73095b5cd96 100644
> --- a/include/linux/ksm.h
> +++ b/include/linux/ksm.h
> @@ -93,6 +93,7 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
> void collect_procs_ksm(const struct folio *folio, const struct page *page,
> struct list_head *to_kill, int force_early);
> long ksm_process_profit(struct mm_struct *);
> +bool ksm_process_mergeable(struct mm_struct *mm);
>
> #else /* !CONFIG_KSM */
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 7ac59cde626c..be2eb1778225 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -3263,6 +3263,25 @@ static void wait_while_offlining(void)
> #endif /* CONFIG_MEMORY_HOTREMOVE */
>
> #ifdef CONFIG_PROC_FS
> +/*
> + * The process is mergeable only if any VMA is currently
> + * applicable to KSM.
> + *
> + * The mmap lock must be held in read mode.
> + */
> +bool ksm_process_mergeable(struct mm_struct *mm)
> +{
> + struct vm_area_struct *vma;
> +
> + mmap_assert_locked(mm);
> + VMA_ITERATOR(vmi, mm, 0);
> + for_each_vma(vmi, vma)
> + if (vma->vm_flags & VM_MERGEABLE)
> + return true;
> +
> + return false;
> +}
> +
> long ksm_process_profit(struct mm_struct *mm)
> {
> return (long)(mm->ksm_merging_pages + mm_ksm_zero_pages(mm)) * PAGE_SIZE -
> --
> 2.15.2
>
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