linux-kernel - Re: [PATCH v2] mm: Fix error handling in __filemap_get_folio() with FGP

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Message-ID: <20250224141744.GA1088@lst.de>
Date: Mon, 24 Feb 2025 15:17:44 +0100
From: Christoph Hellwig <hch@....de>
To: "Raphael S. Carvalho" <raphaelsc@...lladb.com>
Cc: linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	djwong@...nel.org, Dave Chinner <david@...morbit.com>, hch@....de,
	willy@...radead.org
Subject: Re: [PATCH v2] mm: Fix error handling in __filemap_get_folio()
 with FGP_NOWAIT

On Mon, Feb 24, 2025 at 05:13:28AM -0300, Raphael S. Carvalho wrote:
> +		if (err) {
> +			/* Prevents -ENOMEM from escaping to user space with FGP_NOWAIT */
> +			if ((fgp_flags & FGP_NOWAIT) && err == -ENOMEM)
> +				err = -EAGAIN;
>  			return ERR_PTR(err);

I don't think the comment is all that useful.  It's also overly long.

I'd suggest this instead:

			/*
			 * When NOWAIT I/O fails to allocate folios this could
			 * be due to a nonblocking memory allocation and not
			 * because the system actually is out of memory.
			 * Return -EAGAIN so that there caller retries in a
			 * blocking fashion instead of propagating -ENOMEM
			 * to the application.
			 */