[PATCH 10/17] prmem: documentation

[Matthew Wilcox]

On Tue, Oct 30, 2018 at 10:43:14PM +0200, Igor Stoppa wrote:
> On 30/10/2018 21:20, Matthew Wilcox wrote:
> > > > So the API might look something like this:
> > > > 
> > > > 	void *p = rare_alloc(...);	/* writable pointer */
> > > > 	p->a = x;
> > > > 	q = rare_protect(p);		/* read-only pointer */
> 
> With pools and memory allocated from vmap_areas, I was able to say
> 
> protect(pool)
> 
> and that would do a swipe on all the pages currently in use.
> In the SELinux policyDB, for example, one doesn't really want to
> individually protect each allocation.
> 
> The loading phase happens usually at boot, when the system can be assumed to
> be sane (one might even preload a bare-bone set of rules from initramfs and
> then replace it later on, with the full blown set).
> 
> There is no need to process each of these tens of thousands allocations and
> initialization as write-rare.
> 
> Would it be possible to do the same here?

What Andy is proposing effectively puts all rare allocations into
one pool.  Although I suppose it could be generalised to multiple pools
... one mm_struct per pool.  Andy, what do you think to doing that?

> > but we'd probably wrap it in list_for_each_rare_entry(), just to be nicer.
> 
> This seems suspiciously close to the duplication of kernel interfaces that I
> was roasted for :-)

Can you not see the difference between adding one syntactic sugar function
and duplicating the entire infrastructure?