linux-kernel - Re: [PATCH v3 0/4] Make MIGRATE

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Message-ID: <20250508043835.GA320498@cmpxchg.org>
Date: Thu, 8 May 2025 00:38:35 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Zi Yan <ziy@...dia.com>
Cc: David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oscar Salvador <osalvador@...e.de>,
	Vlastimil Babka <vbabka@...e.cz>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	Richard Chang <richardycc@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/4] Make MIGRATE_ISOLATE a standalone bit

On Wed, May 07, 2025 at 05:10:55PM -0400, Zi Yan wrote:
> 
> Hi Johannes,
> 
> I incorporated all your feedback on v2 (see Changelog below), except the
> "decoupling enum migratetype from the pageblock bits" one[1], since all
> 5 migratetypes (not MIGRATE_ISOLATE) are just values and
> "#define PB_migratetype_bits MIGRATE_TYPE_BITS" would take 5 bits
> for migratetypes, which only requires 3 bits. Let me know if I
> misunderstand your suggestion. Thanks.

Right, it's better to stick with enum values. My main worry was that
PB_migratetype_bits *usually* correspond to an enum migratetype, and
MIGRATE_ISOLATE being the precarious exception. But I think it's much
clearer with the special-casing in get/set_pageblock_migratetype()
instead of the lower pfnmask functions. Thanks for moving that!