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From: Chengming Zhou Date: Tue, 28 May 2024 13:15:22 +0800 Subject: [PATCH v3 2/2] mm/ksm: fix ksm_zero_pages accounting MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20240528-b4-ksm-counters-v3-2-34bb358fdc13@linux.dev> References: <20240528-b4-ksm-counters-v3-0-34bb358fdc13@linux.dev> In-Reply-To: <20240528-b4-ksm-counters-v3-0-34bb358fdc13@linux.dev> To: Andrew Morton , David Hildenbrand , hughd@google.com, aarcange@redhat.com, Stefan Roesch , Xiaokai Ran , xu xin , Yang Yang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, zhouchengming@bytedance.com, Chengming Zhou X-Developer-Signature: v=1; a=ed25519-sha256; t=1716873365; l=5017; i=chengming.zhou@linux.dev; s=20240508; h=from:subject:message-id; bh=5jHsxXd8zdPd706tl2Ubj0ZrdiWpVOv9Lxro+6nHmOc=; b=v7pQUR5dWHG0CW3hlK5ixSeteB47vG0GGXUi+MHTgy6Iqr+keE+paN3GabHlhibRUblv0dSGO AwnovP9yUvzDbLg6q0J1JWpPPMHN5l5x5yLDJ4esOLuWg9LtJE6s/ku X-Developer-Key: i=chengming.zhou@linux.dev; a=ed25519; pk=kx40VUetZeR6MuiqrM7kPCcGakk1md0Az5qHwb6gBdU= X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: A09BF40005 X-Stat-Signature: qbam3b3suki8ic7g99ma918rcxzzptnj X-HE-Tag: 1716873380-623970 X-HE-Meta: U2FsdGVkX199WHoW33WKJbhQZGkWBEq9W18W/Yh7YPTiXgq/SChvfbTelqq3iNei2UIUByrYiZo+7KLFe0n9SpBNsgn06QwYxbouKE9FxQOPHz62lW30pjEmdvMxF3T/rY3NB36/zSuhH6opm+CAZDsMQJ2vK+iMfNbJGv6tpS5rzRmI6i8TRawQIizQL6W21ToByh1317jI7/GWmqntONcOomVi81Y9eZyV597KZHIZ65su/YOZ3FEB7QM9JlCm2xtsKi9ml2ZYNq2W8lz/fimVN3xKe38SezgpeqRlZAnLylGWrhQa2VplyOTkZqJK4jwUTPP5Rf8sy1ffXl7cpvR1sBTAS79wqWJw3/Cw/y3XjrVdiX2+5kKegMBCmuk1cj2rR/qIxcGKo6mLVvGAhcSNV5ZxCGSFhGcU8kZVbSS+llmyHPV4vXHoZlwGqPdpmZqS5F4LWigXoA8kq4mJj2AnyrisDar4GDxPcj8LyZd+8qK47XYWa0OAe1o/NaZ6feS+6HWwR1tCad5SmxRd+eoLugGyWQoh9cIFq8MAAErp6LGRMzIKu7eaPDSx8BKvRh9MGcwmbGmUDLoytmc7rAJOpTNLG89wkVy39tF+KS6Ol2DJ54kysHRreWJedwNVYTloGaVt530o/qLHu5D6CEGn+hxJHMKY6aU2n5WVN6xu0CM1ctUc3oK2vOe5QT+LaLI3CvK2s737Ci8v6nULdoMAHgBK848pJB9MYM20d2bZXIQ3IV3BaqNqbn9XT++35YryMvR1PxiPzsiNUxlpsCkIQTV5VdbzDzifMqzTfuF5qc/wmXPlZkJEaJ5LS3qmkqgRLhFq3q5SnMUrnhlRRYZJGawE3qv5OJOxbuqRvlmrBMIYKUO3tgfmKHnRrenwWVx8e3VqNkbgrzAnrQ5ETYMiKhqwMgRrh0F9tCfay+OiJXaHGfeE9ToA4kdV3yNX2HFZKxY2pOZSeIfejoA EpaC0MEB MhSjJ5mqozZBAS73on4MZQ2Nxfyq2+8r3yseOJJJHZpi2nDvzXU8QZ1+X/ofIoU841gcxu8mgaFEeZqtjQaAgXS5W4Tv0tDPW8KcG7+zpnyuQUodzouEXYiUgopm4yhr7+va/IyiNEVDU2rFsvCkQmf8kMzsPsMtnULp3 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: We normally ksm_zero_pages++ in ksmd when page is merged with zero page, but ksm_zero_pages-- is done from page tables side, where there is no any accessing protection of ksm_zero_pages. 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") Acked-by: David Hildenbrand Signed-off-by: Chengming Zhou --- fs/proc/base.c | 2 +- include/linux/ksm.h | 17 ++++++++++++++--- include/linux/mm_types.h | 2 +- mm/ksm.c | 11 +++++------ 4 files changed, 21 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..11690dacd986 100644 --- a/include/linux/ksm.h +++ b/include/linux/ksm.h @@ -33,16 +33,27 @@ 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 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 9e99cb12d330..34c4820e0d3d 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 @@ -3374,7 +3373,7 @@ 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 */ @@ -3663,7 +3662,7 @@ 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", atomic_long_read(&ksm_zero_pages)); } KSM_ATTR_RO(ksm_zero_pages); @@ -3672,7 +3671,7 @@ 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 + atomic_long_read(&ksm_zero_pages)) * PAGE_SIZE - ksm_rmap_items * sizeof(struct ksm_rmap_item); return sysfs_emit(buf, "%ld\n", general_profit); -- 2.45.1