Re: [RFC PATCH v1] mm/vmalloc: fix incorrect __vmap_pages_range_noflush() if vm_area_alloc_pages() from high order fallback to order0

[Hailong.Liu <hailong.liu@oppo.com>]

On Wed, 24. Jul 21:02, Matthew Wilcox wrote:
> On Thu, Jul 25, 2024 at 02:28:27AM +0800, Hailong.Liu wrote:
> > >  	if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
> > > -			page_shift == PAGE_SHIFT)
> > > -		return vmap_small_pages_range_noflush(addr, end, prot, pages);
> > > +			page_shift == PAGE_SHIFT ||
> > > +			page_private(pages[0]) == VM_AREA_ALLOC_PAGES_FALLBACK) {
> > > +		int ret = vmap_small_pages_range_noflush(addr, end, prot, pages);
> > > +
> > > +		set_page_private(pages[0], 0);
> > > +		return ret;
> > > +	}
> > >
> > >  	for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
> > >  		int err;
> > > @@ -3583,6 +3590,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> > >
> > >  			/* fall back to the zero order allocations */
> > >  			alloc_gfp |= __GFP_NOFAIL;
> > > +			fallback = true;
> > Sry for my mistake, I forget define fallback here.
> > BTW, This is not the optimal solution. Does anyone have a better idea? Glad to
> > hear:)
>
> Yeah, I really don't like this approach.  You could return a small
> struct indicating both nr_allocated and whether you had to fall back.
> Or you could pass a bool * parameter.  They're both pretty nasty.
Agree. Thanks for pointing out. I send a rfc-v2 patch with a different solution.
pls help review.
https://lore.kernel.org/all/20240725035318.471-1-hailong.liu@oppo.com/T/#u

--
help you, help me,
Hailong.