Re: [RFC PATCH 2/5] mm, arch: unify vmemmap_populate altmap handling

[Michal Hocko]

On Mon 31-07-17 16:27:46, Gerald Schaefer wrote:
> On Mon, 31 Jul 2017 14:55:56 +0200
> Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> 
> > On Mon 31-07-17 14:40:53, Gerald Schaefer wrote:
> > [...]
> > > > @@ -247,12 +248,12 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
> > > >  			 * use large frames even if they are only partially
> > > >  			 * used.
> > > >  			 * Otherwise we would have also page tables since
> > > > -			 * vmemmap_populate gets called for each section
> > > > +			 * __vmemmap_populate gets called for each section
> > > >  			 * separately. */
> > > >  			if (MACHINE_HAS_EDAT1) {
> > > >  				void *new_page;
> > > > 
> > > > -				new_page = vmemmap_alloc_block(PMD_SIZE, node);
> > > > +				new_page = __vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
> > > >  				if (!new_page)
> > > >  					goto out;
> > > >  				pmd_val(*pm_dir) = __pa(new_page) | sgt_prot;
> > > 
> > > There is another call to vmemmap_alloc_block() in this function, a couple
> > > of lines below, this should also be replaced by __vmemmap_alloc_block_buf().
> > 
> > I've noticed that one but in general I have only transformed PMD
> > mappings because we shouldn't even get to pte level if the forme works
> > AFAICS. Memory sections should be always 2MB aligned unless I am missing
> > something. Or is this not true?
> 
> vmemmap_populate() on s390 will only stop at pmd level if we have HW
> support for large pages (MACHINE_HAS_EDAT1). In that case we will allocate
> a PMD_SIZE block with vmemmap_alloc_block() and map it on pmd level as
> a large page.
> 
> Without HW large page support, we will continue to allocate a pte page,
> populate the pmd entry with that, and fall through to the pte_none()
> check below, with its PAGE_SIZE vmemmap_alloc_block() allocation. In this
> case we should use the __vmemmap_alloc_block_buf().

OK, I see. I've considered s390 will support large pages in general. I
will fold this in. Thanks!
---
commit df13e3a1237c3fef399e26b0f5a015715df12ede
Author: Michal Hocko <mhocko@xxxxxxxx>
Date:   Mon Jul 31 16:34:18 2017 +0200

    fold me "mm, arch: unify vmemmap_populate altmap handling"
    
    - use altmap even for ptes in case the HW doesn't support large pages
      as per Gerald Schaefer

diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index 07120bc137a1..764b6393e66c 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -273,7 +273,7 @@ int __meminit __vmemmap_populate(unsigned long start, unsigned long end, int nod
 		if (pte_none(*pt_dir)) {
 			void *new_page;
 
-			new_page = vmemmap_alloc_block(PAGE_SIZE, node);
+			new_page = __vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
 			if (!new_page)
 				goto out;
 			pte_val(*pt_dir) = __pa(new_page) | pgt_prot;
-- 
Michal Hocko
SUSE Labs