On Tue, Feb 16, 2010 at 10:13:12AM -0800, Chris Frost wrote: > Add the fincore() system call. fincore() is mincore() for file descriptors. > > The functionality of fincore() can be emulated with an mmap(), mincore(), > and munmap(), but this emulation requires more system calls and requires > page table modifications. fincore() can provide a significant performance > improvement for non-sequential in-core queries. In addition to being expensive, mmap/mincore/munmap perturb the VM's eviction algorithm -- a page is less likely to be evicted if it's mmapped when being considered for eviction. I frequently see this happen when using mincore(1) from http://bitbucket.org/radii/mincore/ -- "watch mincore -v *.big" while *.big are being sequentially read results in a significant number of pages remaining in-core, whereas if I only run mincore after the sequential read is complete, the large files will be nearly-completely out of core (except for the tail of the last file, of course). It's very interesting to watch % watch --interval=.5 mincore -v * while an IO-intensive process is happening, such as mke2fs on a filesystem image. So, I support the addition of fincore(2) and would use it if it were merged. -andy -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
