From nobody Fri Apr 10 02:37:39 2026 Received: from fanzine2.igalia.com (fanzine2.igalia.com [213.97.179.56]) (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 059B3382F12 for ; Wed, 4 Mar 2026 20:34:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.97.179.56 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772656450; cv=none; b=ZCuxnleDLP+ipyAC63xxyXBxhwFa9JuCGqk/IR+c2oRjddzOaDX2RVUz7ZcvgVQVkw7ejYoVYGpfeMCF8nRNDZSq5GcXCinYbaul4C+0ns2z6Rt6kUjO2UcvWtmoXblI5f5a7PrzAh2UiwleEt0lbtkK5rMlMLY+7GXyh+kjHJk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772656450; c=relaxed/simple; bh=L5+ydF5S6ZCMVRjeT9+1rLaG1q33L3NEonVNS6NjYw8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OE01QBrLzP74j6vbAg0SSqvPg1VDVjRmhdCpaWJBBaSy/1dZ3Gb463jr0SlyqKM3uL4c+5OQXeFWCNkTPWwKXiaxwunikPY5vkcX/hxThiTKZnRbMyDNmn38Kw3NahhGOUXUF2j/Vg9ahXKyaHcEgF4s+bcGiPhzM7mahL7L8W4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=igalia.com; spf=pass smtp.mailfrom=igalia.com; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b=Np0WFrvU; arc=none smtp.client-ip=213.97.179.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=igalia.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=igalia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b="Np0WFrvU" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:MIME-Version:References:In-Reply-To: Message-ID:Date:Subject:Cc:To:From:Sender:Reply-To:Content-Type:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=6pD4cx+Qs8foK5AODwyhhW7E99pbqcu5bSXgXaDf43Y=; b=Np0WFrvU46WW/Tonff+PtKMIKl BP6b+Q/cy0Evhm/iiw02rzIO1aSULGQLghwd4jD/jWldxrFCH5xs9IXojfjH9XM0cPYyvOFsJX9ou T7yZ7sbbQPba4hDGT+AQS5SZ5GjkBwgAlOhRRw6QhVK7DnkqU59p4YMbzKJZ1yy5B7/qDYDiczpA8 6IwomZRjtoMcdGeWHOvucEbQQdmnl2LCnzPj05PSB9IIsT7nemp9DWM6sEnW5bHRNOTJPeuMnPVwR TYxRGMKK77cIFqxRnIy4i/RM+JEp685ZQJ81KhSb1vOEJdmgv7Qv0GH6p6zND9Yk5KEChr0oap8H1 EowTfv/w==; Received: from [187.90.181.146] (helo=localhost) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1vxsux-0095KN-9M; Wed, 04 Mar 2026 21:34:03 +0100 From: "Guilherme G. Piccoli" To: linux-mm@kvack.org, rppt@kernel.org Cc: linux-kernel@vger.kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net, gpiccoli@igalia.com, Andrew Morton , Steven Rostedt Subject: [PATCH V2 2/2] mm/memblock: Add reserve_mem debugfs info Date: Wed, 4 Mar 2026 17:14:11 -0300 Message-ID: <20260304203300.1414286-4-gpiccoli@igalia.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260304203300.1414286-2-gpiccoli@igalia.com> References: <20260304203300.1414286-2-gpiccoli@igalia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When using the "reserve_mem" parameter, users aim at having an area that (hopefully) persists across boots, so pstore infrastructure (like ramoops module) can make use of that to save oops/ftrace logs, for example. There is no easy way to determine if this kernel parameter is properly set though; the kernel doesn't show information about this memory in memblock debugfs, neither in /proc/iomem nor dmesg. This is a relevant information for tools like kdumpst[0], to determine if it's reliable to use the reserved area as ramoops persistent storage; checking only /proc/cmdline is not sufficient as it doesn't tell if the reservation effectively succeeded or not. Add here a new file under memblock debugfs showing properly set memory reservations, with name and size as passed to "reserve_mem". Notice that if no "reserve_mem=3D" is passed on command-line or if the reservation attempts fail, the file is not created. [0] https://aur.archlinux.org/packages/kdumpst Cc: Andrew Morton Cc: Mike Rapoport Cc: Steven Rostedt Signed-off-by: Guilherme G. Piccoli --- Thanks a lot for the suggestions Mike! I'm not sure if you would prefer a Co-Developed-by or Suggested-by instead of CC, you helped a lot improving the code. Lemme know and either I can re-submit (with potential other changes) or even, you can change while merging. V2: (all suggestions by Mike Rapoport) - Commit message (showing use case); - Drop ifdef on include "string_helpers.h"; - Don't show the address of reserve_mem, only name and size; - Fixed flag names inside ARCH_KEEP_MEMBLOCK ifdef; - Make use of its own show_attribute instead of refactoring the memblock one; - Use sizeof() instead of magical numbers for the size; - Don't show memblock directory if no reserve_mem succeeded and ARCH_KEEP_MEMBLOCK isn't defined (keeping current behavior). mm/memblock.c | 37 +++++++++++++++++++++++++++++++++++-- 1 file changed, 35 insertions(+), 2 deletions(-) diff --git a/mm/memblock.c b/mm/memblock.c index 2d2646f7a120..d816796ab919 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -17,6 +17,7 @@ #include #include #include +#include =20 #ifdef CONFIG_KEXEC_HANDOVER #include @@ -2711,7 +2712,8 @@ static int __init reserve_mem(char *p) } __setup("reserve_mem=3D", reserve_mem); =20 -#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_ARCH_KEEP_MEMBLOCK) +#ifdef CONFIG_DEBUG_FS +#ifdef CONFIG_ARCH_KEEP_MEMBLOCK static const char * const flagname[] =3D { [ilog2(MEMBLOCK_HOTPLUG)] =3D "HOTPLUG", [ilog2(MEMBLOCK_MIRROR)] =3D "MIRROR", @@ -2758,10 +2760,40 @@ static int memblock_debug_show(struct seq_file *m, = void *private) } DEFINE_SHOW_ATTRIBUTE(memblock_debug); =20 +#endif /* CONFIG_ARCH_KEEP_MEMBLOCK */ + +static int memblock_reserve_mem_show(struct seq_file *m, void *private) +{ + struct reserve_mem_table *map; + char txtsz[16]; + + for (int i =3D 0; i < reserved_mem_count; i++) { + map =3D &reserved_mem_table[i]; + if (!map->size) + continue; + + memset(txtsz, 0, sizeof(txtsz)); + string_get_size(map->size, 1, STRING_UNITS_2, txtsz, sizeof(txtsz)); + seq_printf(m, "%s\t\t(%s)\n", map->name, txtsz); + } + + return 0; +} +DEFINE_SHOW_ATTRIBUTE(memblock_reserve_mem); + static int __init memblock_init_debugfs(void) { - struct dentry *root =3D debugfs_create_dir("memblock", NULL); + struct dentry *root; =20 + if (!(IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK) || reserved_mem_count)) + return 0; + + root =3D debugfs_create_dir("memblock", NULL); + + if (reserved_mem_count) + debugfs_create_file("reserve_mem_param", 0444, root, NULL, + &memblock_reserve_mem_fops); +#ifdef CONFIG_ARCH_KEEP_MEMBLOCK debugfs_create_file("memory", 0444, root, &memblock.memory, &memblock_debug_fops); debugfs_create_file("reserved", 0444, root, @@ -2771,6 +2803,7 @@ static int __init memblock_init_debugfs(void) &memblock_debug_fops); #endif =20 +#endif /* CONFIG_ARCH_KEEP_MEMBLOCK */ return 0; } __initcall(memblock_init_debugfs); --=20 2.50.1