linux-kernel - Re: [PATCH 22/43] CacheFiles: Add a hook to write a single page of data to an inode [ver #46]

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Date:	Fri, 03 Apr 2009 14:41:48 +0100
From:	David Howells <dhowells@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>,
	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	dhowells@...hat.com, viro@...iv.linux.org.uk, nfsv4@...ux-nfs.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 22/43] CacheFiles: Add a hook to write a single page of data to an inode [ver #46]

David Howells <dhowells@...hat.com> wrote:

> +			data = kmap(page);
> +			old_fs = get_fs();
> +			set_fs(KERNEL_DS);
> +			ret = file->f_op->write(
> +				file, (const void __user *) data, PAGE_SIZE,
> +				&pos);
> +			set_fs(old_fs);
> +			kunmap(page);

Hmmm...  Now I've thought about it some more, I'm not sure this is a good
idea.  Can this run a system out of kmap() resources?  These are run by a
dynamic thread pool, where each thread in the pool can do a kmap and issue a
write, but the write may get delayed for a significant amount of time for a
number of reasons - such as block allocation, data fetching and memory
allocation.

David
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