On Thu, 2013-02-14 at 01:40 -0500, Johannes Weiner wrote: > On Thu, Feb 14, 2013 at 04:34:28AM +0000, Ben Hutchings wrote: > > Hot-adding memory on x86_64 normally requires huge page allocation. > > When this is done to a VM guest, it's usually because the system is > > already tight on memory, so the request tends to fail. Try to avoid > > this by adding __GFP_REPEAT to the allocation flags. > > > > Reported-and-tested-by: Bernhard Schmidt <Bernhard.Schmidt@xxxxxx> > > Reference: http://bugs.debian.org/699913 > > Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> > > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> > > > We could go even further and use __GFP_NOFAIL, but I'm not sure > > whether that would be a good idea. > > If __GFP_REPEAT is not enough, I'd rather fall back to regular page > backing at this point: Oh yes, I had considered doing that before settling on __GFP_REPEAT. It does seem worth doing. Perhaps you could also log a specific warning, as the use of 4K page entries for this could have a significant performance impact. Ben. > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > index 2ead3c8..1f5301d 100644 > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -919,6 +919,7 @@ vmemmap_populate(struct page *start_page, unsigned long size, int node) > { > unsigned long addr = (unsigned long)start_page; > unsigned long end = (unsigned long)(start_page + size); > + int use_huge = cpu_has_pse; > unsigned long next; > pgd_t *pgd; > pud_t *pud; > @@ -934,8 +935,8 @@ vmemmap_populate(struct page *start_page, unsigned long size, int node) > pud = vmemmap_pud_populate(pgd, addr, node); > if (!pud) > return -ENOMEM; > - > - if (!cpu_has_pse) { > +retry_pmd: > + if (!use_huge) { > next = (addr + PAGE_SIZE) & PAGE_MASK; > pmd = vmemmap_pmd_populate(pud, addr, node); > > @@ -957,8 +958,10 @@ vmemmap_populate(struct page *start_page, unsigned long size, int node) > pte_t entry; > > p = vmemmap_alloc_block_buf(PMD_SIZE, node); > - if (!p) > - return -ENOMEM; > + if (!p) { > + use_huge = 0; > + goto retry_pmd; > + } > > entry = pfn_pte(__pa(p) >> PAGE_SHIFT, > PAGE_KERNEL_LARGE); > -- Ben Hutchings Absolutum obsoletum. (If it works, it's out of date.) - Stafford Beer
Attachment:
signature.asc
Description: This is a digitally signed message part