linux-kernel - Re: [PATCH v2 24/24] ext4: enable block size larger than page size

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Message-ID: <52401c3a-26aa-473f-b7e2-1c658550dd37@pankajraghav.com>
Date: Mon, 10 Nov 2025 13:51:28 +0100
From: Pankaj Raghav <kernel@...kajraghav.com>
To: libaokun@...weicloud.com, linux-ext4@...r.kernel.org
Cc: tytso@....edu, adilger.kernel@...ger.ca, jack@...e.cz,
 linux-kernel@...r.kernel.org, mcgrof@...nel.org, ebiggers@...nel.org,
 willy@...radead.org, yi.zhang@...wei.com, yangerkun@...wei.com,
 chengzhihao1@...wei.com, libaokun1@...wei.com
Subject: Re: [PATCH v2 24/24] ext4: enable block size larger than page size

On 11/7/25 15:42, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
> 
> Since block device (See commit 3c20917120ce ("block/bdev: enable large
> folio support for large logical block sizes")) and page cache (See commit
> ab95d23bab220ef8 ("filemap: allocate mapping_min_order folios in the page
> cache")) has the ability to have a minimum order when allocating folio,
> and ext4 has supported large folio in commit 7ac67301e82f ("ext4: enable
> large folio for regular file"), now add support for block_size > PAGE_SIZE
> in ext4.
> 
> set_blocksize() -> bdev_validate_blocksize() already validates the block
> size, so ext4_load_super() does not need to perform additional checks.
> 
> Here we only need to add the FS_LBS bit to fs_flags.
> 
> In addition, allocation failures for large folios may trigger warn_alloc()
> warnings. Therefore, as with XFS, mark this feature as experimental.
> 

Are you adding the experimental flag because allocation failures can occur with
LBS configuration or because it is a new feature (or both)?

In XFS we added this flag because this was a new feature and not because of the
allocation failure that might happen.

Is it even possible to get rid of these allocation failures in systems were the
memory is limited as the page cache works in > PAGE_SIZE allocations?

--
Pankaj