Re: [RFC PATCH] mm: fadvise: avoid fadvise for fs without backing device

[Andrew Morton]

On Thu, 17 Aug 2017 18:20:17 -0700 Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:

> +linux-mm, linux-kernel
> 
> On Thu, Aug 17, 2017 at 6:10 PM, Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
> > The fadvise() manpage is silent on fadvise()'s effect on
> > memory-based filesystems (shmem, hugetlbfs & ramfs) and pseudo
> > file systems (procfs, sysfs, kernfs). The current implementaion
> > of fadvise is mostly a noop for such filesystems except for
> > FADV_DONTNEED which will trigger expensive remote LRU cache
> > draining. This patch makes the noop of fadvise() on such file
> > systems very explicit.
> >
> > However this change has two side effects for ramfs and one for
> > tmpfs. First fadvise(FADV_DONTNEED) can remove the unmapped clean
> > zero'ed pages of ramfs (allocated through read, readahead & read
> > fault) and tmpfs (allocated through read fault). Also
> > fadvise(FADV_WILLNEED) on create such clean zero'ed pages for
> > ramfs.

That sentence makes no sense.  I assume "fadvise(FADV_WILLNEED) will
create"?