> 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.
