From nobody Sat Feb 7 15:58:23 2026 Received: from out-180.mta1.migadu.com (out-180.mta1.migadu.com [95.215.58.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6CDF67BAF0 for ; Wed, 8 May 2024 09:56:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.180 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715162195; cv=none; b=XPzoLEneKtRbm01VwFbyb8J8dhENjnx6POcFOnBjO6CaC5ggFbF7OgADn+Z/hSxZ4QzkaE6PhXxVWE7O8UVhzmTecowTvWnaEzRYrqesipLWJDC7jY2BNYDtiZN7KK21NDW+WRHCSa9khlB0ZyVZKR01HBFzJbmSY5wy/0gvQYA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715162195; c=relaxed/simple; bh=zT3260cOojJ9YkJT42xnisTrezwzaldkD24iYYJXwwo=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=QiiqpQCjWceF4DGQR5P28yP5td/xhrTWLJDFz+3JPFZ6Qfmu0mOGQba52Yqx0SZPGkKHMWXGNsD8FU5JdcS6LCZxgnf9WnCyT/y3zJDtyIJiSTVTMqdGA3K8qL97Lkeq2jkDlT4P7D/7goucpK+/BkJ2VB9T+jakVlNsWJjR0xo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=sOWryHtG; arc=none smtp.client-ip=95.215.58.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="sOWryHtG" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1715162191; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2bLQ4gptvM3L1QRVzQ/kljeJWLtVefD+oipqeUeshP8=; b=sOWryHtG3kXzk2QHXqC3vWzkFP+FlHnR4lQWZKayTg4D2xGZnkjYjf+0j5aWmIgXNvd7zT 2QTe1nDeX5MKcr4QGAkBy3rzDwzo0dDxHfeOb8oJM+xxOXS9rkqgLYVByDvnSqwIxXy2bs iLs3tqru3cEhRFU15/Fg6ROIvd2+Gv8= From: Chengming Zhou Date: Wed, 08 May 2024 17:55:39 +0800 Subject: [PATCH 2/4] mm/ksm: fix ksm_zero_pages accounting Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20240508-b4-ksm-counters-v1-2-e2a9b13f70c5@linux.dev> References: <20240508-b4-ksm-counters-v1-0-e2a9b13f70c5@linux.dev> In-Reply-To: <20240508-b4-ksm-counters-v1-0-e2a9b13f70c5@linux.dev> To: Andrew Morton , David Hildenbrand , Stefan Roesch , xu xin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, zhouchengming@bytedance.com, Chengming Zhou X-Developer-Signature: v=1; a=ed25519-sha256; t=1715162174; l=4898; i=chengming.zhou@linux.dev; s=20240508; h=from:subject:message-id; bh=zT3260cOojJ9YkJT42xnisTrezwzaldkD24iYYJXwwo=; b=pw9F/6MfqwjmEILvTY9Kw8kVwDgxLbZH1bNRvo778ZsSVX+2PHfvvqg43hSoNnMZZzZZRsU89 AoIeAp0psC8AQfATubxnDjo3cEl5nWUpcfboQr/FSoASz3WAK8siagH X-Developer-Key: i=chengming.zhou@linux.dev; a=ed25519; pk=kx40VUetZeR6MuiqrM7kPCcGakk1md0Az5qHwb6gBdU= X-Migadu-Flow: FLOW_OUT 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 Acked-by: David Hildenbrand --- 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, stru= ct pid_namespace *ns, mm =3D 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)) =20 -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); +} =20 static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t p= te) { 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); } } =20 +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 =3D true; =20 /* The number of zero pages which is placed by KSM */ -unsigned long ksm_zero_pages; +atomic_long_t ksm_zero_pages =3D ATOMIC_LONG_INIT(0); =20 /* 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, s= truct page *page, * the dirty bit in zero page's PTE is set. */ newpte =3D 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); =20 @@ -3671,7 +3670,7 @@ static ssize_t general_profit_show(struct kobject *ko= bj, { long general_profit; =20 - general_profit =3D (ksm_pages_sharing + ksm_zero_pages) * PAGE_SIZE - + general_profit =3D (ksm_pages_sharing + get_ksm_zero_pages()) * PAGE_SIZE= - ksm_rmap_items * sizeof(struct ksm_rmap_item); =20 return sysfs_emit(buf, "%ld\n", general_profit); --=20 2.45.0