linux-kernel - Re: [RFC PATCH] block, fs: use FOLL_LONGTERM as gup

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Message-ID: <14a3ea66-9f11-49fd-a7ee-c04be1d428f5@acm.org>
Date: Wed, 12 Mar 2025 09:03:05 -0700
From: Bart Van Assche <bvanassche@....org>
To: Christoph Hellwig <hch@...radead.org>,
 Suren Baghdasaryan <surenb@...gle.com>
Cc: Sooyong Suk <s.suk@...sung.com>, Jaewon Kim <jaewon31.kim@...il.com>,
 viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
 akpm@...ux-foundation.org, linux-mm@...ck.org, spssyr@...il.com,
 axboe@...nel.dk, linux-block@...r.kernel.org, dhavale@...gle.com
Subject: Re: [RFC PATCH] block, fs: use FOLL_LONGTERM as gup_flags for direct
 IO

On 3/12/25 8:52 AM, Christoph Hellwig wrote:
> I'd still like to understand what the use case is.  Who does CMA
> allocation at a time where heavy direct I/O is in progress?

An additional question: why is contiguous memory allocated? Is this
perhaps because the allocated memory will be used for DMA? If so,
can the SMMU be used to make it appear contiguous to DMA clients?

Thanks,

Bart.