Re: Discard support (was Re: [PATCH] swap: send callback when swapslot is freed)
From: Nitin Gupta
Date: Thu Aug 13 2009 - 12:13:34 EST
On 08/13/2009 08:43 PM, Matthew Wilcox wrote:
I am planning a complete overhaul of the discard work. Users can send
down discard requests as frequently as they like. The block layer will
cache them, and invalidate them if writes come through. Periodically,
the block layer will send down a TRIM or an UNMAP (depending on the
underlying device) and get rid of the blocks that have remained unwanted
in the interim.
This batching of discard requests is still sub-optimal for compcache.
The optimal solution in this case is to get callback *as soon as* a swap
slot becomes free and this is what this patch does.
I see that it will be difficult to accept this patch since compcache
seems to be the only user for now. However, this little addition makes a
*big* difference for the project. Currently, much of memory is wasted to
store all the stale data.
I will be posting compcache patches for review in next merge window. So,
maybe this patch can be included now as the first step? The revised
patch is ready which addresses issues raised during the first review --
will post it soon.
Thanks,
Nitin
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