Re: [RESEND PATCH v1] mm/vmalloc: fix page mapping if vm_area_alloc_pages() with high order fallback to order 0

[Uladzislau Rezki <urezki@gmail.com>]

On Mon, Aug 19, 2024 at 03:38:51PM +0200, Uladzislau Rezki wrote:
> On Mon, Aug 19, 2024 at 08:57:38PM +0800, Hailong Liu wrote:
> > On Mon, 19. Aug 13:59, Uladzislau Rezki wrote:
> > > On Fri, Aug 16, 2024 at 07:46:26PM +0800, Hailong Liu wrote:
> > > > On Fri, 16. Aug 12:13, Uladzislau Rezki wrote:
> > > > > On Fri, Aug 16, 2024 at 05:12:32PM +0800, Hailong Liu wrote:
> > > > > > On Thu, 15. Aug 22:07, Andrew Morton wrote:
> > > > > > > On Fri, 9 Aug 2024 11:41:42 +0200 Uladzislau Rezki <urezki@gmail.com> wrote:
> > > > > > >
> > > > > > > > > > Acked-by: Barry Song <baohua@kernel.org>
> > > > > > > > > >
> > > > > > > > > > because we already have a fallback here:
> > > > > > > > > >
> > > > > > > > > > void *__vmalloc_node_range_noprof :
> > > > > > > > > >
> > > > > > > > > > fail:
> > > > > > > > > >         if (shift > PAGE_SHIFT) {
> > > > > > > > > >                 shift = PAGE_SHIFT;
> > > > > > > > > >                 align = real_align;
> > > > > > > > > >                 size = real_size;
> > > > > > > > > >                 goto again;
> > > > > > > > > >         }
> > > > > > > > >
> > > > > > > > > This really deserves a comment because this is not really clear at all.
> > > > > > > > > The code is also fragile and it would benefit from some re-org.
> > > > > > > > >
> > > > > > > > > Thanks for the fix.
> > > > > > > > >
> > > > > > > > > Acked-by: Michal Hocko <mhocko@suse.com>
> > > > > > > > >
> > > > > > > > I agree. This is only clear for people who know the code. A "fallback"
> > > > > > > > to order-0 should be commented.
> > > > > > >
> > > > > > > It's been a week.  Could someone please propose a fixup patch to add
> > > > > > > this comment?
> > > > > >
> > > > > > Hi Andrew:
> > > > > >
> > > > > > Do you mean that I need to send a v2 patch with the the comments included?
> > > > > >
> > > > > It is better to post v2.
> > > > Got it.
> > > >
> > > > >
> > > > > But before, could you please comment on:
> > > > >
> > > > > in case of order-0, bulk path may easily fail and fallback to the single
> > > > > page allocator. If an request is marked as NO_FAIL, i am talking about
> > > > > order-0 request, your change breaks GFP_NOFAIL for !order.
> > > > >
> > > > > Am i missing something obvious?
> > > > For order-0, alloc_pages(GFP_X | __GFP_NOFAIL, 0), buddy allocator will handle
> > > > the flag correctly. IMO we don't need to handle the flag here.
> > > >
> > > Agree. As for comment, i meant to comment the below fallback:
> > Michal send a craft that make nofail logic more clearer and I check the branch
> > found Andrew already merged in -stable branch. So we can include these with a
> > new patch.
> >
> Just to confirm. Will you send an extra patch with the comment?
> 
Also, an idea to handle NOFAIL outside of vm_area_alloc_pages() looks
sounds good to me.

--
Uladzislau Rezki