Alex Kramarov wrote: > > Hi. > > I have shifted from redhat 7.1 to 7.2, and have several machines running > both versions now. I have noticed, that the memory usage patern is very > different on machines using ext2 and ext3 - the ones using ext2 usually use > 5-10 MB of "buff" memory, but the ones with ext3 grow to 50MB on machines > with 128MB, and to 250MB with on machine with 512 MB. I have conducted a > test, and changed /etc/fstab on the 7.2 machine to mount all partitions ext2 > instead of ext3, and the "buff" memory is back to 5 MB, as with normal 7.1 > linux. > Several months ago, ext2 was changed so that directory contents are held in the pagecache, not the buffercache. We never applied a similar change to ext3. Consequently, buffercache usage (as reported by top, vmstat, free, etc) will be larger with ext3. In ext2, directory caching is lumped into the `cached' figure, not `buffers'. But we're really just caching the data in the same place, under a different name. Given the 2.4.10 unification of the buffercache with the pagecache, there's not much difference now from a caching point of view. It's just that the kernel-internal APIs for getting at the data are different. (And they're more unwieldy for the buffercache case, but ext3 likes to use buffers, and is a *lot* more complex than ext2).
