Messages in this thread | | | Date | Tue, 23 May 2023 11:47:55 +0200 | Subject | Re: [PATCH v8 2/6] ksm: count all zero pages placed by KSM | From | David Hildenbrand <> |
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On 22.05.23 12:52, Yang Yang wrote: > From: xu xin <xu.xin16@zte.com.cn> > > As pages_sharing and pages_shared don't include the number of zero pages > merged by KSM, we cannot know how many pages are zero pages placed by KSM > when enabling use_zero_pages, which leads to KSM not being transparent with > all actual merged pages by KSM. In the early days of use_zero_pages, > zero-pages was unable to get unshared by the ways like MADV_UNMERGEABLE so > it's hard to count how many times one of those zeropages was then unmerged. > > But now, unsharing KSM-placed zero page accurately has been achieved, so we > can easily count both how many times a page full of zeroes was merged with > zero-page and how many times one of those pages was then unmerged. and so, > it helps to estimate memory demands when each and every shared page could > get unshared. > > So we add ksm_zero_pages under /sys/kernel/mm/ksm/ to show the number > of all zero pages placed by KSM. > > v7->v8: > Handle the case when khugepaged replaces a shared zeropage by a THP. > > Signed-off-by: xu xin <xu.xin16@zte.com.cn> > Suggested-by: David Hildenbrand <david@redhat.com> > Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> > Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn> > Reviewed-by: Xiaokai Ran <ran.xiaokai@zte.com.cn> > Reviewed-by: Yang Yang <yang.yang29@zte.com.cn> > --- > include/linux/ksm.h | 17 +++++++++++++++++ > mm/khugepaged.c | 3 +++ > mm/ksm.c | 12 ++++++++++++ > mm/memory.c | 7 ++++++- > 4 files changed, 38 insertions(+), 1 deletion(-) > > diff --git a/include/linux/ksm.h b/include/linux/ksm.h > index 7989200cdbb7..1adcae0205e3 100644 > --- a/include/linux/ksm.h > +++ b/include/linux/ksm.h > @@ -29,6 +29,16 @@ void __ksm_exit(struct mm_struct *mm); > /* use pte_mkdirty to track a KSM-placed zero page */ > #define set_pte_ksm_zero(pte) pte_mkdirty(pte_mkspecial(pte)) > #define is_ksm_zero_pte(pte) (is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte)) > +extern unsigned long ksm_zero_pages; > +static inline void inc_ksm_zero_pages(void) > +{ > + ksm_zero_pages++; > +} > +
No need to export the inc, just inline this.
> +static inline void dec_ksm_zero_pages(void) > +{ > + ksm_zero_pages--; > +} > > static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm) > { > @@ -100,6 +110,13 @@ static inline void ksm_exit(struct mm_struct *mm) > > #define set_pte_ksm_zero(pte) pte_mkspecial(pte) > #define is_ksm_zero_pte(pte) 0 > +static inline void inc_ksm_zero_pages(void) > +{ > +} > + > +static inline void dec_ksm_zero_pages(void) > +{ > +} > > #ifdef CONFIG_MEMORY_FAILURE > static inline void collect_procs_ksm(struct page *page, > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 6b9d39d65b73..ba0d077b6951 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -19,6 +19,7 @@ > #include <linux/page_table_check.h> > #include <linux/swapops.h> > #include <linux/shmem_fs.h> > +#include <linux/ksm.h> > > #include <asm/tlb.h> > #include <asm/pgalloc.h> > @@ -711,6 +712,8 @@ static void __collapse_huge_page_copy_succeeded(pte_t *pte, > spin_lock(ptl); > ptep_clear(vma->vm_mm, address, _pte); > spin_unlock(ptl); > + if (is_ksm_zero_pte(pteval)) > + dec_ksm_zero_pages(); > } > } else { > src_page = pte_page(pteval); > diff --git a/mm/ksm.c b/mm/ksm.c > index 9962f5962afd..2ca7e8860faa 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -278,6 +278,9 @@ static unsigned int zero_checksum __read_mostly; > /* Whether to merge empty (zeroed) pages with actual zero pages */ > static bool ksm_use_zero_pages __read_mostly; > > +/* The number of zero pages which is placed by KSM */ > +unsigned long ksm_zero_pages; > + > #ifdef CONFIG_NUMA > /* Zeroed when merging across nodes is not allowed */ > static unsigned int ksm_merge_across_nodes = 1; > @@ -1223,6 +1226,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, > } else { > newpte = set_pte_ksm_zero(pfn_pte(page_to_pfn(kpage), > vma->vm_page_prot)); > + inc_ksm_zero_pages(); > /* > * We're replacing an anonymous page with a zero page, which is > * not anonymous. We need to do proper accounting otherwise we > @@ -3350,6 +3354,13 @@ static ssize_t pages_volatile_show(struct kobject *kobj, > } > KSM_ATTR_RO(pages_volatile); > > +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); > +} > +KSM_ATTR_RO(ksm_zero_pages); > + > static ssize_t general_profit_show(struct kobject *kobj, > struct kobj_attribute *attr, char *buf) > { > @@ -3417,6 +3428,7 @@ static struct attribute *ksm_attrs[] = { > &pages_sharing_attr.attr, > &pages_unshared_attr.attr, > &pages_volatile_attr.attr, > + &ksm_zero_pages_attr.attr, > &full_scans_attr.attr, > #ifdef CONFIG_NUMA > &merge_across_nodes_attr.attr, > diff --git a/mm/memory.c b/mm/memory.c > index 8358f3b853f2..058b416adf24 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1415,8 +1415,11 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, > tlb_remove_tlb_entry(tlb, pte, addr); > zap_install_uffd_wp_if_needed(vma, addr, pte, details, > ptent); > - if (unlikely(!page)) > + if (unlikely(!page)) { > + if (is_ksm_zero_pte(ptent)) > + dec_ksm_zero_pages(); > continue; > + } > > delay_rmap = 0; > if (!PageAnon(page)) { > @@ -3120,6 +3123,8 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf) > inc_mm_counter(mm, MM_ANONPAGES); > } > } else { > + if (is_ksm_zero_pte(vmf->orig_pte)) > + dec_ksm_zero_pages(); > inc_mm_counter(mm, MM_ANONPAGES); > } > flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
Can we maybe avoid exporting the dec semantics and rather add a callback to KSM? Ideally, we'd even distill that down to a single call, and handle the details in ksm.h. Maybe simply:
ksm_notify_unmap_zero_page(vmf->orig_pte);
and then just have in ksm.h
static inline void ksm_notify_unmap_zero_page(pte_t pte) { if (is_ksm_zero_pte(pte)) ksm_zero_pages--; }
-- Thanks,
David / dhildenb
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