linux-kernel - Re: [PATCH 22/25] fs/buffer: prevent WARN_ON in __alloc_pages

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Message-ID: <aPxV6QnXu-OufSDH@casper.infradead.org>
Date: Sat, 25 Oct 2025 05:45:29 +0100
From: Matthew Wilcox <willy@...radead.org>
To: libaokun@...weicloud.com
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
	jack@...e.cz, linux-kernel@...r.kernel.org, kernel@...kajraghav.com,
	mcgrof@...nel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, yi.zhang@...wei.com, yangerkun@...wei.com,
	chengzhihao1@...wei.com, libaokun1@...wei.com
Subject: Re: [PATCH 22/25] fs/buffer: prevent WARN_ON in
 __alloc_pages_slowpath() when BS > PS

On Sat, Oct 25, 2025 at 11:22:18AM +0800, libaokun@...weicloud.com wrote:
> +	while (1) {
> +		folio = __filemap_get_folio(mapping, index, fgp_flags,
> +					    gfp & ~__GFP_NOFAIL);
> +		if (!IS_ERR(folio) || !(gfp & __GFP_NOFAIL))
> +			return folio;
> +
> +		if (PTR_ERR(folio) != -ENOMEM && PTR_ERR(folio) != -EAGAIN)
> +			return folio;
> +
> +		memalloc_retry_wait(gfp);
> +	}

No, absolutely not.  We're not having open-coded GFP_NOFAIL semantics.
The right way forward is for ext4 to use iomap, not for buffer heads
to support large block sizes.