On Thu, 2005-07-14 at 19:29 -0400, Mark Hahn wrote: > > i also want a way to clear part of the whole page cache by file id. :) > > understandably, kernel developers are don't high-prioritize this sort of > not-useful-for-normal-work feature. agree. > > > i also want a way to tell the cache distribution, how many for file A > > and B, .... > > you should probably try mmaping the file and using mincore. > come to think of it, mmap+madvise might be a sensible way to > flush pages corresponding to a particular file, as well. i prefer a generic way. :) it will be useful to tune the system. maybe write a program to iterate the kernel structure can do this. > > > > I'm really surprised there isn't something in /proc you can use to > > > clear or disable the cache. Would be very useful for benchmarking! > > I assume you noticed "blockdev --flushbufs", no? it works for me > (ie, a small, repeated streaming read of a disk device will show > pagecache speed). it will do flush right? but will it flush and clean cache? > > I think the problem is that it's difficult to dissociate readahead, > writebehind and normal lru-ish caching. there was quite a flurry of > activity around 2.4.10 related to this, and it left a bad taste in > everyone's mouth. I think the main conclusion was that too much fanciness > results in a fragile, more subtle and difficult-to-maintain system > that performs better, true, but over a narrower range of workloads. maybe this will happen again for 2.6.x? i think there are still many gray areas that can be checked. also many places can be improved. a test i did show that even you have sda and sdb to form a raid0, the page cache for sda and sdb will not be used by raid0. kind of funny. > > regards, mark hahn > sharcnet/mcmaster. > thx! Ming - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
