From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 35DAFCA6019 for ; Fri, 9 Oct 2026 11:23:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C665D6B008C; Fri, 9 Oct 2026 07:23:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BF1076B0092; Fri, 9 Oct 2026 07:23:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B05416B0096; Fri, 9 Oct 2026 07:23:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 822596B008C for ; Fri, 9 Oct 2026 07:23:36 -0400 (EDT) Received: from smtpin15.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 18E0EC0322 for ; Fri, 9 Oct 2026 11:23:36 +0000 (UTC) X-FDA: 85302852432.15.0DF2521 Received: from mail-m82120.xmail.ntesmail.com (mail-m82120.xmail.ntesmail.com [156.224.82.120]) by imf21.hostedemail.com (Postfix) with ESMTP id 50C051C0006 for ; Fri, 9 Oct 2026 11:23:32 +0000 (UTC) Authentication-Results: imf21.hostedemail.com; dkim=none; spf=pass (imf21.hostedemail.com: domain of zhen.ni@easystack.cn designates 156.224.82.120 as permitted sender) smtp.mailfrom=zhen.ni@easystack.cn; dmarc=pass (policy=none) header.from=easystack.cn ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1791545014; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WcC0Dtp9m4em3Iqmcx7fHXo32hpC93JJyX0q33wUHZs=; b=VOA2XFuPY2+NC48ds1tvRbiQ6UXd2ozevHCDxjG/8tECab5tfmL5oFPfKMGWxd0uRDjSxV 5rjvfqRZUR7ixtMLyV9mbmUa+TD8Tl9xMn0SbvnLCkG2LH/UGPz3aRoaILFOEp4xeGUV7c s4xm/J4x3rcnHZPBt2or7o3b/hAho2I= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1791545014; b=7fWxLv5+Ic10SFfQZrUmtr49ylx0MuQJXyLUC6usspHRohpYeDvbdCmp6WDvEa7kE6osfG e4oWxd3eHDnZgNZaLnyAZ28aJJSQagV3yWjLDRCf3Hz7oImB6USNAC4lDkdp6dDNnUczzW R9RwRyR0rMk1FKH2INUs2+PlG8y/K44= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=none; spf=pass (imf21.hostedemail.com: domain of zhen.ni@easystack.cn designates 156.224.82.120 as permitted sender) smtp.mailfrom=zhen.ni@easystack.cn; dmarc=pass (policy=none) header.from=easystack.cn Received: from localhost.localdomain (unknown [218.94.118.90]) by smtp.qiye.163.com (Hmail) with ESMTP id 1fe29019f; Fri, 9 Oct 2026 19:23:25 +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 1/6] mm/page_owner: extract page_owner_next_eligible() from read loop Date: Fri, 9 Oct 2026 19:23:03 +0800 Message-Id: <20261009112308.240769-2-zhen.ni@easystack.cn> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20261009112308.240769-1-zhen.ni@easystack.cn> References: <20261009112308.240769-1-zhen.ni@easystack.cn> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-HM-Tid: 0aa1206756430229kunmd33b3e054cb27c X-HM-MType: 1 X-HM-Spam-Status: e1kfGhgUHx5ZQUpXWQgPGg8OCBgUHx5ZQUlOS1dZFg8aDwILHllBWSg2Ly tZV1koWUFJQjdXWRgWCB1ZQUpXWS1ZQUlXWQ8JGhUIEh9ZQVlCSRlMVh8dSEsZQ0tJGh9KT1YVFA kWGhdVGRETFhoSFyQUDg9ZV1kYEgtZQVlJSkNVQk9VSkpDVUJLWVdZFhoPEhUdFFlBWU9LSFVKS0 lPT09IVUpLS1VKQktLWQY+ X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 50C051C0006 X-Stat-Signature: pmfdm7h8ujjdj6jzzq65nn7jfmaucwg4 X-HE-Tag: 1791545012-277476 X-HE-Meta: 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 nSlaZ93N Mfz8+NZ+PykD4EFz2kFB08BxAyncwmVfdzb1MF9S4/IouxftH4Om5PPrVqLa/xP6AwnHrA/rqOBy9YGFzBLOw+7rBCq3nDy2YcgtygnPFPglGbneXLU+czCWjRYDfpZe72waPZ/6oDbHDmidMp+e0uKM6HA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 --- mm/page_owner.c | 105 ++++++++++++++++++++++++++++++------------------ 1 file changed, 66 insertions(+), 39 deletions(-) diff --git a/mm/page_owner.c b/mm/page_owner.c index fbbda7ba914b..bafe474f3360 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) - goto ext_put_continue; + scan->pfn = pfn; + scan->page = page; + scan->po_snap = *page_owner; + page_ext_put(page_ext); + if (!scan->po_snap.handle) + continue; + + 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