From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 DE5553B4E8C for ; Mon, 29 Jun 2026 08:00:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782720044; cv=none; b=Ay4E9A+wOKDDluPTEt29SZU6NP6wVYjo6E0WrwwpFAj5DVjAiMT+MIJeqCPfpgr6C2Nu1/hEYNcUR/bYEjhF6kgA0h5+WDKJvQABRbOsCo/BT4hbpp7Rn35QDK3omLuuzfLfU7eqfwKe5D8sbleWl5wSc47tuPMJlwDHOt/mirs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782720044; c=relaxed/simple; bh=LaNPnONXr4cOVkR4GvP7rEFQyFUSRhsLXM42DFI/h4Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HW3tEMdQXTRWMjf92pVvUCn8fakk2Hf1cacOOqpA+TJyiYXW2sJYbdezLjFTrBRRkctkrUzRzkDuRoODB9ZyFK2UHPMpthjpTWvenr4kfNOe5wjeVZIlEQCgoRw7zfxIWnW0njOYDRPTUQbiCEjoucm2nSdDFNbWWrD9CJtcHPY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EXKS81pj; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="EXKS81pj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C7F691F000E9; Mon, 29 Jun 2026 08:00:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782720042; bh=W/LgCWWfF/NcaocAuaVXtNR665KgEcQqH4uB4RpU4cw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=EXKS81pjhnX/T3t20HwM0r+G8lZqOaf7LUBFI4WeNo8HO7Dv9KyGrHaNmXneQ778Z dREeqYHE7e/A5Q+YYwlBlEMv0GobGewa87N0nTR3ppXR/wdBGeAjiI6pjGNSvoMDN0 eZ6UoSXLBoe4MqtKJ4Sl/waE+QXU1BcmAB2ZLjoDSlVhukD+jGCRfVjgbQLsrg0Q7G 3k8082FO++Ml3PQ2eE9k8jCQ/sgc7mfHWX1HgRPZFp3B6oAdg/kxrJoZ4WXe7GELHG an6aeydeJMc45Q290ZgCuvu/l80ioKCKwq5n9oHNf2QpIySP7ObpJ94ugAT9Lw7qtT bvUZsyYFN24uA== Message-ID: Date: Mon, 29 Jun 2026 10:00:39 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/6] mm/page_owner: use MIGRATE_REASON_NONE instead of -1 for last_migrate_reason Content-Language: en-US To: Ye Liu , Zi Yan , Andrew Morton Cc: Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260626024550.25677-1-ye.liu@linux.dev> <20260626024550.25677-3-ye.liu@linux.dev> <407fa67f-3212-4c5a-ac8c-7c5d41479cc9@linux.dev> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/29/26 04:20, Ye Liu wrote: > > > 在 2026/6/27 02:45, Zi Yan 写道: >> On Thu Jun 25, 2026 at 10:45 PM EDT, Ye Liu wrote: >>> The last_migrate_reason field uses -1 as a sentinel value to mean "no >>> migration has happened". Replace the four bare -1 occurrences with a >>> local MIGRATE_REASON_NONE define so the intent is explicit and the >>> magic number is eliminated. >>> >>> No functional change. >>> >>> Signed-off-by: Ye Liu >>> --- >>> mm/page_owner.c | 15 +++++++++++---- >>> 1 file changed, 11 insertions(+), 4 deletions(-) >>> >>> diff --git a/mm/page_owner.c b/mm/page_owner.c >>> index 342549891a8d..ebafa9d7ff07 100644 >>> --- a/mm/page_owner.c >>> +++ b/mm/page_owner.c >>> @@ -21,6 +21,13 @@ >>> */ >>> #define PAGE_OWNER_STACK_DEPTH (16) >>> >>> +/* >>> + * Used to indicate that a page has never been migrated, as the valid >>> + * migrate_reason values are non-negative enum members (MR_* in >>> + * include/linux/migrate_mode.h). >> >> Why not change last_migrate_reason to enum migrate_reason and functions >> pass migrate reasons? MR_TYPES probably can be used to indicate no >> migration has happened if we do not want to add MR_NO_MIGRATION. Indeed. I'd just add a proper MR_NEVER option with a comment. >> folio_set_owner_migrate_reason(), >> __folio_set_owner_migrate_reason(), >> move_hugetlb_state(), and >> __update_page_owner_handle() need to update their signatures for this. They should ideally, but do they "need" as part of this series? But I guess it's not a big deal. > Thanks for the review. > > Using MR_TYPES as a sentinel is problematic - it's used kernel-wide as an > array-size marker (migrate_reason_names[MR_TYPES]). Overloading it to also > mean "never migrated" conflates two unrelated semantics. It also has a Well it's just for tracepoint and dumping page owner. Nothing prevents us assigning a value to MR_NEVER that's not -1 (just make MR_NEVER the first or last option of the enum) and a give it a name e.g. "never_migrated" in include/trace/events/migrate.h > subtle out-of-bounds risk: if anyone ever uses the field as an array index > without the guard check, MR_TYPES silently points past the end of the array, > while -1 faults immediately. That wouldn't be a problem either with a proper value. > Adding MR_NONE = -1 to the enum is the right long-term fix, but that needs > proper enum definition changes and cascading signature updates across multiple > headers — better done as a separate series. > The current patch is a minimal improvement: it kills the magic number and > makes intent explicit without touching any header. Minimal fixes are sometimes necessary for actual bugs, for stable backport etc. Nothing prevents us doing it properly here. >> >>> + */ >>> +#define MIGRATE_REASON_NONE (-1) >>> + >>> struct page_owner { >>> unsigned short order; >>> short last_migrate_reason; >>> @@ -339,7 +346,7 @@ noinline void __set_page_owner(struct page *page, unsigned short order, >>> depot_stack_handle_t handle; >>> >>> handle = save_stack(gfp_mask); >>> - __update_page_owner_handle(page, handle, order, gfp_mask, -1, >>> + __update_page_owner_handle(page, handle, order, gfp_mask, MIGRATE_REASON_NONE, >>> ts_nsec, current->pid, current->tgid, >>> current->comm); >>> inc_stack_record_count(handle, gfp_mask, 1 << order); >>> @@ -596,7 +603,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, >>> if (ret >= count) >>> goto err; >>> >>> - if (page_owner->last_migrate_reason != -1) { >>> + if (page_owner->last_migrate_reason != MIGRATE_REASON_NONE) { >>> ret += scnprintf(kbuf + ret, count - ret, >>> "Page has been migrated, last migrate reason: %s\n", >>> migrate_reason_names[page_owner->last_migrate_reason]); >>> @@ -667,7 +674,7 @@ void __dump_page_owner(const struct page *page) >>> stack_depot_print(handle); >>> } >>> >>> - if (page_owner->last_migrate_reason != -1) >>> + if (page_owner->last_migrate_reason != MIGRATE_REASON_NONE) >>> pr_alert("page has been migrated, last migrate reason: %s\n", >>> migrate_reason_names[page_owner->last_migrate_reason]); >>> page_ext_put(page_ext); >>> @@ -826,7 +833,7 @@ static void init_pages_in_zone(struct zone *zone) >>> >>> /* Found early allocated page */ >>> __update_page_owner_handle(page, early_handle, 0, 0, >>> - -1, local_clock(), current->pid, >>> + MIGRATE_REASON_NONE, local_clock(), current->pid, >>> current->tgid, current->comm); >>> count++; >>> ext_put_continue: >> >> >> >> >