Re: [PATCH v9 0/8] stg mail -e --version=v9 \

[Michael S. Tsirkin]

On Wed, Sep 11, 2019 at 01:36:19PM +0200, Michal Hocko wrote:
> On Tue 10-09-19 14:23:40, Alexander Duyck wrote:
> [...]
> > We don't put any limitations on the allocator other then that it needs to
> > clean up the metadata on allocation, and that it cannot allocate a page
> > that is in the process of being reported since we pulled it from the
> > free_list. If the page is a "Reported" page then it decrements the
> > reported_pages count for the free_area and makes sure the page doesn't
> > exist in the "Boundary" array pointer value, if it does it moves the
> > "Boundary" since it is pulling the page.
> 
> This is still a non-trivial limitation on the page allocation from an
> external code IMHO. I cannot give any explicit reason why an ordering on
> the free list might matter (well except for page shuffling which uses it
> to make physical memory pattern allocation more random) but the
> architecture seems hacky and dubious to be honest. It shoulds like the
> whole interface has been developed around a very particular and single
> purpose optimization.
> 
> I remember that there was an attempt to report free memory that provided
> a callback mechanism [1], which was much less intrusive to the internals
> of the allocator yet it should provide a similar functionality. Did you
> see that approach? How does this compares to it? Or am I completely off
> when comparing them?
> 
> [1] mostly likely not the latest version of the patchset
> http://lkml.kernel.org/r/1502940416-42944-5-git-send-email-wei.w.wang@xxxxxxxxx
> 
> -- 
> Michal Hocko
> SUSE Labs

Linus nacked that one. He thinks invoking callbacks with lots of
internal mm locks is too fragile.