From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-m1973198.qiye.163.com (mail-m1973198.qiye.163.com [220.197.31.98]) (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 C5DF013D53C; Tue, 13 Oct 2026 12:57:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=220.197.31.98 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791896246; cv=none; b=HCVcBussIkwz+T7P3gu7SrXHjKkcJ1DTZR4KjrvlllnEozgi+fb2bj4SX+SRqVY5WA4+VEPmqBYoT5Z6qNvrkDdtBJATb6k52jeArI9FiIl4aibulEVDKoxl0twPWcgztFUJW/iSmPdDSk8ipRHoSF9L2yA2H7Iv4Jl8U0Y9FQo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791896246; c=relaxed/simple; bh=mCsPqGiqz9PyjMkewqXOYz3BEsU6ovphopKLLemF7Gw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=usw4tkVF03O74JkU/lKL38zZUrQE44OneE1IiTeONsuP1DWD/wmMGH08/ASuM2pZ2gfKae/ySFN7ChYkZ4NRrZzEdgZSwO05MYLhx1XGppQm1GV/XI4gYprh+pZO9xqsnu0qHYMiXCiM9/x33caOlUQJO3KReVkLv59s7uFQTjE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=easystack.cn; spf=pass smtp.mailfrom=easystack.cn; arc=none smtp.client-ip=220.197.31.98 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=easystack.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=easystack.cn Received: from localhost.localdomain (unknown [218.94.118.90]) by smtp.qiye.163.com (Hmail) with ESMTP id 200407eea; Tue, 13 Oct 2026 20:21:43 +0800 (GMT+08:00) From: Zhen Ni To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, emil@etsalapatis.com, ihor.solodrai@linux.dev, akpm@linux-foundation.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com, brendan.jackman@linux.dev, hannes@cmpxchg.org, ziy@nvidia.com, shuah@kernel.org Cc: bpf@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Zhen Ni Subject: [PATCH v2 1/6] mm/page_owner: extract page_owner_next_eligible() from read loop Date: Tue, 13 Oct 2026 20:21:20 +0800 Message-Id: <20261013122125.843451-2-zhen.ni@easystack.cn> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20261013122125.843451-1-zhen.ni@easystack.cn> References: <20261013122125.843451-1-zhen.ni@easystack.cn> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-HM-Tid: 0aa1353625140229kunm0bc94a6a524c X-HM-MType: 1 X-HM-Spam-Status: e1kfGhgUHx5ZQUpXWQgPGg8OCBgUHx5ZQUlOS1dZFg8aDwILHllBWSg2Ly tZV1koWUFJQjdXWRgWCB1ZQUpXWS1ZQUlXWQ8JGhUIEh9ZQVkaHRhMVklNTUtNSx0YSh9DGFYVFA kWGhdVGRETFhoSFyQUDg9ZV1kYEgtZQVlJSkNVQk9VSkpDVUJLWVdZFhoPEhUdFFlBWU9LSFVKS0 lPT09IVUpLS1VKQktLWQY+ Move the page scanning logic out of read_page_owner() into a dedicated helper, in preparation for using it in the page_owner bpf_iter target. The helper advances a struct page_owner_scan cursor to the next page eligible for page_owner output and returns true on a hit. On a hit it takes a snapshot of the page_owner record inside the page_ext RCU window. No change to the output is intended. handle is read from the snapshot, taken before the non-zero check, so the validated and reported handle are the same value. Signed-off-by: Zhen Ni --- Changes in v2: - Route the zero-handle case through ext_put_continue. v1: https://lore.kernel.org/linux-mm/20261009112308.240769-2-zhen.ni@easystack.cn/ --- mm/page_owner.c | 103 ++++++++++++++++++++++++++++++------------------ 1 file changed, 65 insertions(+), 38 deletions(-) diff --git a/mm/page_owner.c b/mm/page_owner.c index fbbda7ba914b..56c75a669a6b 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -36,6 +36,16 @@ struct page_owner { pid_t free_tgid; }; +/* + * Cursor and per-page result of page_owner_next_eligible(). + */ +struct page_owner_scan { + /* resume point */ + unsigned long pfn; + struct page *page; + struct page_owner po_snap; +}; + struct stack { struct stack_record *stack_record; struct stack *next; @@ -725,37 +735,24 @@ void __dump_page_owner(const struct page *page) page_ext_put(page_ext); } -static ssize_t -read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) +/* + * Advance @scan to the next page eligible for page_owner output. + * On a hit, fill scan->pfn/page/po_snap and return true; the caller + * must advance scan->pfn past the hit before calling again to resume + * the scan. + */ +static bool page_owner_next_eligible(struct page_owner_scan *scan) { - unsigned long pfn; - struct page *page; - struct page_ext *page_ext; - struct page_owner *page_owner; - depot_stack_handle_t handle; - struct page_owner_filter_state *state = file->private_data; + unsigned long pfn = scan->pfn; - if (!static_branch_unlikely(&page_owner_inited)) - return -EINVAL; - - page = NULL; - if (*ppos == 0) - pfn = min_low_pfn; - else - pfn = *ppos; /* Find a valid PFN or the start of a MAX_ORDER_NR_PAGES area */ while (!pfn_valid(pfn) && (pfn & (MAX_ORDER_NR_PAGES - 1)) != 0) pfn++; - /* Find an allocated page */ for (; pfn < max_pfn; pfn++) { - /* - * This temporary page_owner is required so - * that we can avoid the context switches while holding - * the rcu lock and copying the page owner information to - * user through copy_to_user() or GFP_KERNEL allocations. - */ - struct page_owner page_owner_tmp; + struct page_owner *page_owner; + struct page_ext *page_ext; + struct page *page; /* * If the new page is in a new MAX_ORDER_NR_PAGES area, @@ -798,37 +795,67 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) goto ext_put_continue; /* - * Access to page_ext->handle isn't synchronous so we should - * be careful to access it. + * Take a snapshot of the page_owner record inside the RCU + * window, then validate it, so that print_page_owner() + * reads the checked handle from the same snapshot. */ - handle = READ_ONCE(page_owner->handle); - if (!handle) + scan->pfn = pfn; + scan->page = page; + scan->po_snap = *page_owner; + + if (!scan->po_snap.handle) goto ext_put_continue; + page_ext_put(page_ext); + return true; + +ext_put_continue: + page_ext_put(page_ext); + cond_resched(); + } + + return false; +} + +static ssize_t +read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) +{ + struct page_owner_scan scan; + struct page_owner_filter_state *state = file->private_data; + + if (!static_branch_unlikely(&page_owner_inited)) + return -EINVAL; + + if (*ppos == 0) + scan.pfn = min_low_pfn; + else + scan.pfn = *ppos; + + /* Find an allocated page */ + while (page_owner_next_eligible(&scan)) { if (state->nid_filter_enabled) { int nid; - memdesc_flags_t page_flags = READ_ONCE(page->flags); + memdesc_flags_t page_flags = + READ_ONCE(scan.page->flags); /* * Bypass PF_POISONED_CHECK() in page_to_nid() to avoid * VM_BUG_ON when accessing poisoned pages. */ if (page_flags.f == PAGE_POISON_PATTERN) - goto ext_put_continue; + goto skip_continue; nid = memdesc_nid(&page_flags); if (!node_isset(nid, state->nid_filter)) - goto ext_put_continue; + goto skip_continue; } /* Record the next PFN to read in the file offset */ - *ppos = pfn + 1; + *ppos = scan.pfn + 1; - page_owner_tmp = *page_owner; - page_ext_put(page_ext); - return print_page_owner(buf, count, pfn, page, - &page_owner_tmp, handle, state); -ext_put_continue: - page_ext_put(page_ext); + return print_page_owner(buf, count, scan.pfn, scan.page, + &scan.po_snap, scan.po_snap.handle, state); +skip_continue: + scan.pfn++; cond_resched(); } -- 2.20.1