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Date: Wed, 22 Jul 2026 11:43:50 +0200
From: Christoph Hellwig <hch@lst.de>
To: Matthew Brost <matthew.brost@intel.com>
Cc: intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Hugh Dickins <hughd@google.com>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christian Koenig <christian.koenig@amd.com>,
	Huang Rui <ray.huang@amd.com>,
	Matthew Auld <matthew.auld@intel.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>, Simona Vetter <simona@ffwll.ch>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 1/2] mm/shmem: add shmem_backup_folio() helper
Message-ID: <20260722094350.GA1057@lst.de>
References: <20260721174723.1039395-1-matthew.brost@intel.com>
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In-Reply-To: <20260721174723.1039395-1-matthew.brost@intel.com>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Tue, Jul 21, 2026 at 10:47:22AM -0700, Matthew Brost wrote:
> Add a new generic helper, shmem_backup_folio(), that copies the pages
> of an arbitrary source folio into a range of a shmem-backed file,
> optionally issuing writeback for each destination folio. It is
> extracted from drivers/gpu/drm/ttm's existing shmem-backup loop so
> that other subsystems (starting with TTM in a follow-up patch) can
> share the same implementation.

Hmm, what is the difference to just doing a ITER_BVEC write with a bvec
containing the folio for this the pure write to shmem part of this?

You'd probably want a kernel_write_iter helper wrapping
__kernel_write_iter for the writecount, but otherwise this sounds
like a normal write.

We'd want something for the writeback part, preferably a purely
range based API to be generic.