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

Michal Hocko
2024-08-16T12:33:00Z

On Fri 16-08-24 19:46:26, 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.

Let me clarify what I would like to have clarified:

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 6b783baf12a1..fea90a39f5c5 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3510,13 +3510,13 @@ void *vmap_pfn(unsigned long *pfns, unsigned int count, pgprot_t prot)
EXPORT_SYMBOL_GPL(vmap_pfn);
#endif /* CONFIG_VMAP_PFN */

+/* GFP_NOFAIL semantic is implemented by __vmalloc_node_range_noprof */
static inline unsigned int
vm_area_alloc_pages(gfp_t gfp, int nid,
unsigned int order, unsigned int nr_pages, struct page **pages)
{
unsigned int nr_allocated = 0;
- gfp_t alloc_gfp = gfp;
- bool nofail = gfp & __GFP_NOFAIL;
+ gfp_t alloc_gfp = gfp & ~ __GFP_NOFAIL;
struct page *page;
int i;

@@ -3527,9 +3527,6 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
* more permissive.
*/
if (!order) {
- /* bulk allocator doesn't support nofail req. officially */
- gfp_t bulk_gfp = gfp & ~__GFP_NOFAIL;
-
while (nr_allocated < nr_pages) {
unsigned int nr, nr_pages_request;

@@ -3547,12 +3544,12 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
* but mempolicy wants to alloc memory by interleaving.
*/
if (IS_ENABLED(CONFIG_NUMA) && nid == NUMA_NO_NODE)
- nr = alloc_pages_bulk_array_mempolicy_noprof(bulk_gfp,
+ nr = alloc_pages_bulk_array_mempolicy_noprof(alloc_gfp,
nr_pages_request,
pages + nr_allocated);

else
- nr = alloc_pages_bulk_array_node_noprof(bulk_gfp, nid,
+ nr = alloc_pages_bulk_array_node_noprof(alloc_gfp, nid,
nr_pages_request,
pages + nr_allocated);

@@ -3566,13 +3563,6 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
if (nr != nr_pages_request)
break;
}
- } else if (gfp & __GFP_NOFAIL) {
- /*
- * Higher order nofail allocations are really expensive and
- * potentially dangerous (pre-mature OOM, disruptive reclaim
- * and compaction etc.
- */
- alloc_gfp &= ~__GFP_NOFAIL;
}

/* High-order pages or fallback path if "bulk" fails. */
--
Michal Hocko
SUSE Labs