Re: [RFC PATCH v2] mm/vmalloc: fix incorrect __vmap_pages_range_noflush() if vm_area_alloc_pages() from high order fallback to order0

[Baoquan He]

Hi Barry,

On 07/26/24 at 03:53pm, Barry Song wrote:
> On Fri, Jul 26, 2024 at 2:31 PM Baoquan He <bhe@xxxxxxxxxx> wrote:
......
> >  mm/mm_init.c <<alloc_large_system_hash>>
> >  table = vmalloc_huge(size, gfp_flags);
> >  net/ipv4/inet_hashtables.c <<inet_pernet_hashinfo_alloc>>
> >  new_hashinfo->ehash = vmalloc_huge(ehash_entries * sizeof(struct inet_ehash_bucket),
> >  net/ipv4/udp.c <<udp_pernet_table_alloc>>
> >  udptable->hash = vmalloc_huge(hash_entries * 2 * sizeof(struct udp_hslot)
> >
> > Maybe we should add code comment or document to notice people that the
> > contiguous physical pages are not guaranteed for vmalloc_huge() if you
> > use it after boot.
> 
> Currently, the issue goes beyond just 'contiguous physical pages are
> not guaranteed.'
> The problem includes the likelihood of failure when trying to allocate
> 2MB of contiguous
> memory. That's why I suggest we allow fallback to order-0 for
> non-nofail allocations with
> your proposed changes.

I missed this part of your comment, I agree with you. I think it's doable
with below draft patch combined with my earlier draft change.


diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 260897b21b11..9ae85342d337 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3581,11 +3581,11 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
 		else
 			page = alloc_pages_node_noprof(nid, alloc_gfp, order);
 		if (unlikely(!page)) {
-			if (!nofail)
+			if (!nofail && !order)
 				break;
 
 			/* fall back to the zero order allocations */
-			alloc_gfp |= __GFP_NOFAIL;
+			alloc_gfp = gfp;
 			order = 0;
 			continue;
 		}


Hi Hailong,

Please feel free to collect them to post formal patch, maybe two
patches, one is to allow non-nofail to fallback to order-0 in
vm_area_alloc_pages(), the other is passing out the fallbacked
page_order to vmap_pages_range() if it's OK.

Thanks
Baoquan