Re: [PATCH 08/17] prmem: struct page: track vmap_area

[Matthew Wilcox <willy@infradead.org>]

On Thu, Oct 25, 2018 at 02:01:02AM +0300, Igor Stoppa wrote:
> > > @@ -1747,6 +1750,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
> > >   	if (!addr)
> > >   		return NULL;
> > > +	va = __find_vmap_area((unsigned long)addr);
> > > +	for (i = 0; i < va->vm->nr_pages; i++)
> > > +		va->vm->pages[i]->area = va;
> > 
> > I don't like it that you're calling this for _every_ vmalloc() caller
> > when most of them will never use this.  Perhaps have page->va be initially
> > NULL and then cache the lookup in it when it's accessed for the first time.
> > 
> 
> If __find_vmap_area() was part of the API, this loop could be left out from
> __vmalloc_node_range() and the user of the allocation could initialize the
> field, if needed.
> 
> What is the reason for keeping __find_vmap_area() private?

Well, for one, you're walking the rbtree without holding the spinlock,
so you're going to get crashes.  I don't see why we shouldn't export
find_vmap_area() though.

Another way we could approach this is to embed the vmap_area in the
vm_struct.  It'd require a bit of juggling of the alloc/free paths in
vmalloc, but it might be worthwhile.