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From: David Howells <dhowells@redhat.com>
In-Reply-To: <29524.1238696291@redhat.com>
References: <29524.1238696291@redhat.com> <20090402165505.GA21859@infradead.org> <200904030100.05741.nickpiggin@yahoo.com.au> <200904030232.59355.nickpiggin@yahoo.com.au> <20090402163712.GA25177@infradead.org> <200904030347.21470.nickpiggin@yahoo.com.au>
To: Christoph Hellwig <hch@infradead.org>,
       Nick Piggin <nickpiggin@yahoo.com.au>
Cc: dhowells@redhat.com, viro@zeniv.linux.org.uk, nfsv4@linux-nfs.org,
       linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 22/43] CacheFiles: Add a hook to write a single page of data to an inode [ver #46]
Date: Fri, 03 Apr 2009 14:41:48 +0100
Message-ID: <10789.1238766108@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 895
Lines: 24

David Howells <dhowells@redhat.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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