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Date: Wed, 12 Jun 2024 06:02:16 +0200
From: Christoph Hellwig <hch@lst.de>
To: Shaun Tancheff <shaun.tancheff@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>, Shaun Tancheff <shaun.tancheff@hpe.com>,
	Trond Myklebust <trond.myklebust@hammerspace.com>,
	Anna Schumaker <anna@kernel.org>,
	Matthew Wilcox <willy@infradead.org>, linux-nfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 1/2] filemap: Convert generic_perform_write() to
 support large folios
Message-ID: <20240612040216.GA25886@lst.de>
References: <20240527163616.1135968-1-hch@lst.de> <20240527163616.1135968-2-hch@lst.de> <8e23be47-e542-4bb8-8da7-da7801c98e42@hpe.com> <20240611161311.GA12257@lst.de> <1d87741b-7178-4791-aca2-da3ac3033552@gmail.com>
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On Wed, Jun 12, 2024 at 08:41:01AM +0700, Shaun Tancheff wrote:
> On 6/11/24 23:13, Christoph Hellwig wrote:
>
>> On Tue, Jun 11, 2024 at 05:47:12PM +0700, Shaun Tancheff wrote:
>>>>    	const struct address_space_operations *a_ops = mapping->a_ops;
>>>> +	size_t chunk = mapping_max_folio_size(mapping);
>>> Better to default chunk to PAGE_SIZE for backward compat
>>> +?????? size_t chunk = PAGE_SIZE;
>>>
>>>>    	long status = 0;
>>>>    	ssize_t written = 0;
>>>>    
>>> Have fs opt in to large folio support:
>>>
>>> +?????? if (mapping_large_folio_support(mapping))
>>> +?????????????? chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER;
>> I don't think you've actually read the code, have you?
>
> I checked from 6.6 to linux-next with this patch and my ext4 VM does not boot without the opt-in.

Please take a look at the definition of mapping_max_folio_size,
which is called above in the quoted patch.