linux-kernel - Re: [PATCHv3 02/11] drm/i915/gem: Convert __shmem

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Message-ID: <Z5zcXyYfXSI0PYBY@casper.infradead.org>
Date: Fri, 31 Jan 2025 14:21:19 +0000
From: Matthew Wilcox <willy@...radead.org>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Chris Wilson <chris@...is-wilson.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	"Jason A. Donenfeld" <Jason@...c4.com>,
	Andi Shyti <andi.shyti@...ux.intel.com>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Christian Brauner <brauner@...nel.org>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	David Airlie <airlied@...il.com>,
	David Hildenbrand <david@...hat.com>, Hao Ge <gehao@...inos.cn>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Josef Bacik <josef@...icpanda.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Miklos Szeredi <miklos@...redi.hu>, Nhat Pham <nphamcs@...il.com>,
	Oscar Salvador <osalvador@...e.de>,
	Ran Xiaokai <ran.xiaokai@....com.cn>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Simona Vetter <simona@...ll.ch>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	Vlastimil Babka <vbabka@...e.cz>,
	Yosry Ahmed <yosryahmed@...gle.com>, Yu Zhao <yuzhao@...gle.com>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCHv3 02/11] drm/i915/gem: Convert __shmem_writeback() to
 folios

On Thu, Jan 30, 2025 at 12:00:40PM +0200, Kirill A. Shutemov wrote:
> Use folios instead of pages.
> 
> This is preparation for removing PG_reclaim.

Well, this is a horrid little function.  Rather than iterating just the
dirty folios, it iterates all folios, then locks them before checking
whether they're dirty.

I don't know whether the comments are correct or the code is correct.
This comment doesn't match with setting PageReclaim:

         * Leave mmapings intact (GTT will have been revoked on unbinding,
         * leaving only CPU mmapings around) and add those pages to the LRU
         * instead of invoking writeback so they are aged and paged out
         * as normal.

so I wonder if Chris was confused about what PageReclaim actually does.
Let's find out if he still remembers what he thought it did!