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Date: Fri, 14 Jun 2024 11:21:48 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Trond Myklebust <trondmy@kernel.org>, Anna Schumaker <anna@kernel.org>,
 Steve French <sfrench@samba.org>, linux-nfs@vger.kernel.org,
 linux-cifs@vger.kernel.org, linux-mm@kvack.org, Barry Song
 <v-songbaohua@oppo.com>, Ryan Roberts <ryan.roberts@arm.com>
Subject: Re: [PATCH] nfs: fix nfs_swap_rw for large-folio swap
Message-Id: <20240614112148.cd1961e84b736060c54bdf26@linux-foundation.org>
In-Reply-To: <20240614100329.1203579-2-hch@lst.de>
References: <20240614100329.1203579-1-hch@lst.de>
	<20240614100329.1203579-2-hch@lst.de>
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On Fri, 14 Jun 2024 12:03:25 +0200 Christoph Hellwig <hch@lst.de> wrote:

> As of Linux 6.10-rc the MM can swap out larger than page size chunks.
> NFS has all code ready to handle this, but has a VM_BUG_ON that
> triggers when this happens.  Simply remove the VM_BUG_ON to fix this
> use case.
> 
> ...
>
> --- a/fs/nfs/direct.c
> +++ b/fs/nfs/direct.c
> @@ -141,8 +141,6 @@ int nfs_swap_rw(struct kiocb *iocb, struct iov_iter *iter)
>  {
>  	ssize_t ret;
>  
> -	VM_BUG_ON(iov_iter_count(iter) != PAGE_SIZE);
> -
>  	if (iov_iter_rw(iter) == READ)
>  		ret = nfs_file_direct_read(iocb, iter, true);
>  	else

I'm thinking this should precede "mm: swap: entirely map large folios
found in swapcache", or be a part of it.

Barry/Chuanhua, any opinions?