replaced by new patch from ..

Posted Sep 29, 2005 21:08 UTC (Thu) by nix (subscriber, #2304)
In reply to: replaced by new patch from .. by liljencrantz
Parent article: Swap prefetching

It doesn't fix reading-cache-killers: they'll still push other data out of the cache.

But it handles the other half of the job. :)

replaced by new patch from ..

Posted Sep 29, 2005 21:35 UTC (Thu) by giraffedata (guest, #1954) [Link] (1 responses)

The early writing of dirty pages patch doesn't actually address, except in an incidental way, the problem of single-use pages, either read or write. If you read or write a gigabyte of virtual memory on a .5 gigabyte system, you will sweep physical memory with the patch just like without. To solve that problem, you need to change the cache replacement policy, not the prewriting policy.

Actually, as VM changes so frequently, I don't know just what the present cache replacement policy is; maybe it's already sweep resistant; my point is that early writing isn't about that.

Early writing makes it so all those page frames wasted with pages that will never be used again are at least clean, so when they do get reclaimed, the reclaimer doesn't have to wait. The wait for page laundry is shifted to the guy diryting pages away from the innocent bystander competing for real memory.

replaced by new patch from ..

Posted Sep 29, 2005 23:24 UTC (Thu) by farnz (subscriber, #17727) [Link]

AIUI, the big gain of Andrea's early write-out patch is that the VM has a strong preference for evicting clean pages (nearly free) over dirty (expensive I/O needed). Because Andrea's code stops streaming writes like cp from dirtying lots of one-use pages, it makes the pages that cp is dirtying much more attractive to the VM when it's hunting for freeable pages.