On Thu, Jul 25, 2024 at 8:02 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> 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.
Yes, I feel returning a bool won't work very well.
the result could be a mixture of PMD and PTE if the allocated pages are
larger than a PMD.
For example, if we allocate 8MB, it might result in the first 4MB being
2* PMD, and the remaining 4MB being PTE order-0 pages.
I am also curious what will happen if we allocate 3MB(1PMD + some PTEs),
is the below doing the correct mapping?
do {
ret = vmap_pages_range(addr, addr + size, prot, area->pages,
page_shift);
if (nofail && (ret < 0))
schedule_timeout_uninterruptible(1);
} while (nofail && (ret < 0));
Is it possible we have only mapped the first 2MB if page_shift is PMD?
Thanks
Barry
