On 20/04/10 04:24 PM, Mark Lord wrote:
On 19/04/10 12:20 PM, Greg Freemyer wrote:
Adding Mark Lord in cc.
..
On Mon, Apr 19, 2010 at 6:55 AM, Lukas Czerner<lczerner@xxxxxxxxxx>
wrote:
..
The basic idea behind my discard support is to create an ioctl which
walks through all the free extents in each allocating group and discard
those extents. As an addition to improve its performance one can specify
minimum free extent length, so ioctl will not bother with shorter
extents.
..
Perfect. I proposed exactly this last year, but never found time to work it further.
Please proceed with it!
..
Ahh. here it is/was:
On August 17, 1009, Mark Lord wrote:
Taking care of mounted RAID / LVM filesystems requires in-kernel TRIM
support, possibly exported via an ioctl().
Taking care of unmounted RAID / LVM filesystems is possible in userland,
but would also benefit from in-kernel support, where layouts are defined
and known better than in userland.
The XFS_TRIM was an idea that Cristoph floated, as a concept for examination.
I think something along those lines would be best, but perhaps with an
interface at the VFS layer. Something that permits a userland tool
to work like this (below) might be nearly ideal:
main() {
int fd = open(filesystem_device);
while (1) {
int g, ngroups = ioctl(fd, GET_NUMBER_OF_BLOCK_GROUPS);
for (g = 0; g < ngroups; ++g) {
ioctl(fd, TRIM_ALL_FREE_EXTENTS_OF_GROUP, g);
}
sleep(3600);
}
}
Not all filesystems have a "block group", or "allocation group" structure,
but I suspect that it's an easy mapping in most cases.
With this scheme, the kernel is absolved of the need to track/coallesce
TRIM requests entirely.
Something like that, perhaps.
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