| Message ID | 20240508-b4-ksm-counters-v1-2-e2a9b13f70c5@linux.dev (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/ksm: fix some accounting problems | expand |
On 2024/5/8 17:55, Chengming Zhou wrote: > We normally ksm_zero_pages++ in ksmd when page is merged with zero page, > but ksm_zero_pages-- is done from page tables side, which can't protected > by the ksmd mutex. > > So we can read very exceptional value of ksm_zero_pages in rare cases, > such as -1, which is very confusing to users. > > Fix it by changing to use atomic_long_t, and the same case with the > mm->ksm_zero_pages. > Fixes: e2942062e01d ("ksm: count all zero pages placed by KSM") Fixes: 6080d19f0704 ("ksm: add ksm zero pages for each process") > Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev> > --- > fs/proc/base.c | 2 +- > include/linux/ksm.h | 22 +++++++++++++++++++--- > include/linux/mm_types.h | 2 +- > mm/ksm.c | 11 +++++------ > 4 files changed, 26 insertions(+), 11 deletions(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index 18550c071d71..72a1acd03675 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -3214,7 +3214,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns, > mm = get_task_mm(task); > if (mm) { > seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items); > - seq_printf(m, "ksm_zero_pages %lu\n", mm->ksm_zero_pages); > + 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)); > mmput(mm); > diff --git a/include/linux/ksm.h b/include/linux/ksm.h > index 52c63a9c5a9c..bfc2cf756b0d 100644 > --- a/include/linux/ksm.h > +++ b/include/linux/ksm.h > @@ -33,16 +33,32 @@ void __ksm_exit(struct mm_struct *mm); > */ > #define is_ksm_zero_pte(pte) (is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte)) > > -extern unsigned long ksm_zero_pages; > +extern atomic_long_t ksm_zero_pages; > + > +static inline void ksm_map_zero_page(struct mm_struct *mm) > +{ > + atomic_long_inc(&ksm_zero_pages); > + atomic_long_inc(&mm->ksm_zero_pages); > +} > > static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte) > { > if (is_ksm_zero_pte(pte)) { > - ksm_zero_pages--; > - mm->ksm_zero_pages--; > + atomic_long_dec(&ksm_zero_pages); > + atomic_long_dec(&mm->ksm_zero_pages); > } > } > > +static inline long get_ksm_zero_pages(void) > +{ > + return atomic_long_read(&ksm_zero_pages); > +} > + > +static inline long mm_ksm_zero_pages(struct mm_struct *mm) > +{ > + return atomic_long_read(&mm->ksm_zero_pages); > +} > + > static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm) > { > if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags)) > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 24323c7d0bd4..af3a0256fa93 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -985,7 +985,7 @@ struct mm_struct { > * Represent how many empty pages are merged with kernel zero > * pages when enabling KSM use_zero_pages. > */ > - unsigned long ksm_zero_pages; > + atomic_long_t ksm_zero_pages; > #endif /* CONFIG_KSM */ > #ifdef CONFIG_LRU_GEN_WALKS_MMU > struct { > diff --git a/mm/ksm.c b/mm/ksm.c > index 0f9c491552ff..6e0dca3cecf3 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -296,7 +296,7 @@ static bool ksm_use_zero_pages __read_mostly; > static bool ksm_smart_scan = true; > > /* The number of zero pages which is placed by KSM */ > -unsigned long ksm_zero_pages; > +atomic_long_t ksm_zero_pages = ATOMIC_LONG_INIT(0); > > /* The number of pages that have been skipped due to "smart scanning" */ > static unsigned long ksm_pages_skipped; > @@ -1429,8 +1429,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, > * the dirty bit in zero page's PTE is set. > */ > newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot))); > - ksm_zero_pages++; > - mm->ksm_zero_pages++; > + ksm_map_zero_page(mm); > /* > * We're replacing an anonymous page with a zero page, which is > * not anonymous. We need to do proper accounting otherwise we > @@ -3373,7 +3372,7 @@ static void wait_while_offlining(void) > #ifdef CONFIG_PROC_FS > long ksm_process_profit(struct mm_struct *mm) > { > - return (long)(mm->ksm_merging_pages + mm->ksm_zero_pages) * PAGE_SIZE - > + return (long)(mm->ksm_merging_pages + mm_ksm_zero_pages(mm)) * PAGE_SIZE - > mm->ksm_rmap_items * sizeof(struct ksm_rmap_item); > } > #endif /* CONFIG_PROC_FS */ > @@ -3662,7 +3661,7 @@ KSM_ATTR_RO(pages_skipped); > static ssize_t ksm_zero_pages_show(struct kobject *kobj, > struct kobj_attribute *attr, char *buf) > { > - return sysfs_emit(buf, "%ld\n", ksm_zero_pages); > + return sysfs_emit(buf, "%ld\n", get_ksm_zero_pages()); > } > KSM_ATTR_RO(ksm_zero_pages); > > @@ -3671,7 +3670,7 @@ static ssize_t general_profit_show(struct kobject *kobj, > { > long general_profit; > > - general_profit = (ksm_pages_sharing + ksm_zero_pages) * PAGE_SIZE - > + general_profit = (ksm_pages_sharing + get_ksm_zero_pages()) * PAGE_SIZE - > ksm_rmap_items * sizeof(struct ksm_rmap_item); > > return sysfs_emit(buf, "%ld\n", general_profit); >
On 08.05.24 11:55, Chengming Zhou wrote: > We normally ksm_zero_pages++ in ksmd when page is merged with zero page, > but ksm_zero_pages-- is done from page tables side, which can't protected > by the ksmd mutex. > > So we can read very exceptional value of ksm_zero_pages in rare cases, > such as -1, which is very confusing to users. > > Fix it by changing to use atomic_long_t, and the same case with the > mm->ksm_zero_pages. > > Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev> > --- > fs/proc/base.c | 2 +- > include/linux/ksm.h | 22 +++++++++++++++++++--- > include/linux/mm_types.h | 2 +- > mm/ksm.c | 11 +++++------ > 4 files changed, 26 insertions(+), 11 deletions(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index 18550c071d71..72a1acd03675 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -3214,7 +3214,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns, > mm = get_task_mm(task); > if (mm) { > seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items); > - seq_printf(m, "ksm_zero_pages %lu\n", mm->ksm_zero_pages); > + 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)); > mmput(mm); > diff --git a/include/linux/ksm.h b/include/linux/ksm.h > index 52c63a9c5a9c..bfc2cf756b0d 100644 > --- a/include/linux/ksm.h > +++ b/include/linux/ksm.h > @@ -33,16 +33,32 @@ void __ksm_exit(struct mm_struct *mm); > */ > #define is_ksm_zero_pte(pte) (is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte)) > > -extern unsigned long ksm_zero_pages; > +extern atomic_long_t ksm_zero_pages; > + > +static inline void ksm_map_zero_page(struct mm_struct *mm) > +{ > + atomic_long_inc(&ksm_zero_pages); > + atomic_long_inc(&mm->ksm_zero_pages); > +} > > static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte) > { > if (is_ksm_zero_pte(pte)) { > - ksm_zero_pages--; > - mm->ksm_zero_pages--; > + atomic_long_dec(&ksm_zero_pages); > + atomic_long_dec(&mm->ksm_zero_pages); > } > } > > +static inline long get_ksm_zero_pages(void) > +{ > + return atomic_long_read(&ksm_zero_pages); > +} I suggest inlining that one. The naming of the function also is a bit inconsistent staring at the others. > + > +static inline long mm_ksm_zero_pages(struct mm_struct *mm) > +{ > + return atomic_long_read(&mm->ksm_zero_pages); > +} > + Apart from that LGTM Acked-by: David Hildenbrand <david@redhat.com>
On 2024/5/8 20:36, David Hildenbrand wrote: > On 08.05.24 11:55, Chengming Zhou wrote: >> We normally ksm_zero_pages++ in ksmd when page is merged with zero page, >> but ksm_zero_pages-- is done from page tables side, which can't protected >> by the ksmd mutex. >> >> So we can read very exceptional value of ksm_zero_pages in rare cases, >> such as -1, which is very confusing to users. >> >> Fix it by changing to use atomic_long_t, and the same case with the >> mm->ksm_zero_pages. >> >> Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev> >> --- >> fs/proc/base.c | 2 +- >> include/linux/ksm.h | 22 +++++++++++++++++++--- >> include/linux/mm_types.h | 2 +- >> mm/ksm.c | 11 +++++------ >> 4 files changed, 26 insertions(+), 11 deletions(-) >> >> diff --git a/fs/proc/base.c b/fs/proc/base.c >> index 18550c071d71..72a1acd03675 100644 >> --- a/fs/proc/base.c >> +++ b/fs/proc/base.c >> @@ -3214,7 +3214,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns, >> mm = get_task_mm(task); >> if (mm) { >> seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items); >> - seq_printf(m, "ksm_zero_pages %lu\n", mm->ksm_zero_pages); >> + 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)); >> mmput(mm); >> diff --git a/include/linux/ksm.h b/include/linux/ksm.h >> index 52c63a9c5a9c..bfc2cf756b0d 100644 >> --- a/include/linux/ksm.h >> +++ b/include/linux/ksm.h >> @@ -33,16 +33,32 @@ void __ksm_exit(struct mm_struct *mm); >> */ >> #define is_ksm_zero_pte(pte) (is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte)) >> -extern unsigned long ksm_zero_pages; >> +extern atomic_long_t ksm_zero_pages; >> + >> +static inline void ksm_map_zero_page(struct mm_struct *mm) >> +{ >> + atomic_long_inc(&ksm_zero_pages); >> + atomic_long_inc(&mm->ksm_zero_pages); >> +} >> static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte) >> { >> if (is_ksm_zero_pte(pte)) { >> - ksm_zero_pages--; >> - mm->ksm_zero_pages--; >> + atomic_long_dec(&ksm_zero_pages); >> + atomic_long_dec(&mm->ksm_zero_pages); >> } >> } >> +static inline long get_ksm_zero_pages(void) >> +{ >> + return atomic_long_read(&ksm_zero_pages); >> +} > > I suggest inlining that one. The naming of the function also is a bit inconsistent staring at the others. Good point, I will inline it. > >> + >> +static inline long mm_ksm_zero_pages(struct mm_struct *mm) >> +{ >> + return atomic_long_read(&mm->ksm_zero_pages); >> +} >> + > > Apart from that LGTM > > Acked-by: David Hildenbrand <david@redhat.com> > Thanks!
diff --git a/fs/proc/base.c b/fs/proc/base.c index 18550c071d71..72a1acd03675 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -3214,7 +3214,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns, mm = get_task_mm(task); if (mm) { seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items); - seq_printf(m, "ksm_zero_pages %lu\n", mm->ksm_zero_pages); + 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)); mmput(mm); diff --git a/include/linux/ksm.h b/include/linux/ksm.h index 52c63a9c5a9c..bfc2cf756b0d 100644 --- a/include/linux/ksm.h +++ b/include/linux/ksm.h @@ -33,16 +33,32 @@ void __ksm_exit(struct mm_struct *mm); */ #define is_ksm_zero_pte(pte) (is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte)) -extern unsigned long ksm_zero_pages; +extern atomic_long_t ksm_zero_pages; + +static inline void ksm_map_zero_page(struct mm_struct *mm) +{ + atomic_long_inc(&ksm_zero_pages); + atomic_long_inc(&mm->ksm_zero_pages); +} static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte) { if (is_ksm_zero_pte(pte)) { - ksm_zero_pages--; - mm->ksm_zero_pages--; + atomic_long_dec(&ksm_zero_pages); + atomic_long_dec(&mm->ksm_zero_pages); } } +static inline long get_ksm_zero_pages(void) +{ + return atomic_long_read(&ksm_zero_pages); +} + +static inline long mm_ksm_zero_pages(struct mm_struct *mm) +{ + return atomic_long_read(&mm->ksm_zero_pages); +} + static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm) { if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags)) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 24323c7d0bd4..af3a0256fa93 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -985,7 +985,7 @@ struct mm_struct { * Represent how many empty pages are merged with kernel zero * pages when enabling KSM use_zero_pages. */ - unsigned long ksm_zero_pages; + atomic_long_t ksm_zero_pages; #endif /* CONFIG_KSM */ #ifdef CONFIG_LRU_GEN_WALKS_MMU struct { diff --git a/mm/ksm.c b/mm/ksm.c index 0f9c491552ff..6e0dca3cecf3 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -296,7 +296,7 @@ static bool ksm_use_zero_pages __read_mostly; static bool ksm_smart_scan = true; /* The number of zero pages which is placed by KSM */ -unsigned long ksm_zero_pages; +atomic_long_t ksm_zero_pages = ATOMIC_LONG_INIT(0); /* The number of pages that have been skipped due to "smart scanning" */ static unsigned long ksm_pages_skipped; @@ -1429,8 +1429,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, * the dirty bit in zero page's PTE is set. */ newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot))); - ksm_zero_pages++; - mm->ksm_zero_pages++; + ksm_map_zero_page(mm); /* * We're replacing an anonymous page with a zero page, which is * not anonymous. We need to do proper accounting otherwise we @@ -3373,7 +3372,7 @@ static void wait_while_offlining(void) #ifdef CONFIG_PROC_FS long ksm_process_profit(struct mm_struct *mm) { - return (long)(mm->ksm_merging_pages + mm->ksm_zero_pages) * PAGE_SIZE - + return (long)(mm->ksm_merging_pages + mm_ksm_zero_pages(mm)) * PAGE_SIZE - mm->ksm_rmap_items * sizeof(struct ksm_rmap_item); } #endif /* CONFIG_PROC_FS */ @@ -3662,7 +3661,7 @@ KSM_ATTR_RO(pages_skipped); static ssize_t ksm_zero_pages_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { - return sysfs_emit(buf, "%ld\n", ksm_zero_pages); + return sysfs_emit(buf, "%ld\n", get_ksm_zero_pages()); } KSM_ATTR_RO(ksm_zero_pages); @@ -3671,7 +3670,7 @@ static ssize_t general_profit_show(struct kobject *kobj, { long general_profit; - general_profit = (ksm_pages_sharing + ksm_zero_pages) * PAGE_SIZE - + general_profit = (ksm_pages_sharing + get_ksm_zero_pages()) * PAGE_SIZE - ksm_rmap_items * sizeof(struct ksm_rmap_item); return sysfs_emit(buf, "%ld\n", general_profit);
We normally ksm_zero_pages++ in ksmd when page is merged with zero page, but ksm_zero_pages-- is done from page tables side, which can't protected by the ksmd mutex. So we can read very exceptional value of ksm_zero_pages in rare cases, such as -1, which is very confusing to users. Fix it by changing to use atomic_long_t, and the same case with the mm->ksm_zero_pages. Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev> --- fs/proc/base.c | 2 +- include/linux/ksm.h | 22 +++++++++++++++++++--- include/linux/mm_types.h | 2 +- mm/ksm.c | 11 +++++------ 4 files changed, 26 insertions(+), 11 deletions(-)