On 06/16/2010 03:57 AM, Nick Piggin wrote:
On Tue, Jun 15, 2010 at 03:13:09PM -0400, Rik van Riel wrote:
On 06/15/2010 12:54 PM, Christoph Hellwig wrote:
On Tue, Jun 15, 2010 at 12:49:49PM -0400, Rik van Riel wrote:
This is already in a filesystem. Why does ->writepage get
called a second time? Shouldn't this have a gfp_mask
without __GFP_FS set?
Why would it? GFP_NOFS is not for all filesystem code, but only for
code where we can't re-enter the filesystem due to deadlock potential.
Why? How about because you know the stack is not big enough
to have the XFS call path on it twice? :)
Isn't the whole purpose of this patch series to prevent writepage
from being called by the VM, when invoked from a deep callstack
like xfs writepage?
That sounds a lot like simply wanting to not have GFP_FS...
buffered write path uses __GFP_FS by design because huge amounts
of (dirty) memory can be allocated in doing pagecache writes. If
would be nasty if that was not allowed to wait for filesystem
activity.
__GFP_IO can wait for filesystem activity
__GFP_FS can kick off new filesystem activity
At least, that's how I remember it from when I last looked
at that code in detail. Things may have changed subtly.
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