Re: [PATCH 39 of 66] memcg huge memory

[Andrea Arcangeli]

On Fri, Nov 19, 2010 at 10:19:38AM +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 03 Nov 2010 16:28:14 +0100
> Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote:
> > @@ -402,9 +408,15 @@ static int do_huge_pmd_wp_page_fallback(
> >  	for (i = 0; i < HPAGE_PMD_NR; i++) {
> >  		pages[i] = alloc_page_vma(GFP_HIGHUSER_MOVABLE,
> >  					  vma, address);
> > -		if (unlikely(!pages[i])) {
> > -			while (--i >= 0)
> > +		if (unlikely(!pages[i] ||
> > +			     mem_cgroup_newpage_charge(pages[i], mm,
> > +						       GFP_KERNEL))) {
> > +			if (pages[i])
> >  				put_page(pages[i]);
> > +			while (--i >= 0) {
> > +				mem_cgroup_uncharge_page(pages[i]);
> > +				put_page(pages[i]);
> > +			}
> 
> Maybe you can use batched-uncharge here.
> ==
> mem_cgroup_uncharge_start()
> {
> 	do loop;
> }
> mem_cgroup_uncharge_end();
> ==
> Then, many atomic ops can be reduced.

Cute!

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -413,10 +413,12 @@ static int do_huge_pmd_wp_page_fallback(
 						       GFP_KERNEL))) {
 			if (pages[i])
 				put_page(pages[i]);
+			mem_cgroup_uncharge_start();
 			while (--i >= 0) {
 				mem_cgroup_uncharge_page(pages[i]);
 				put_page(pages[i]);
 			}
+			mem_cgroup_uncharge_end();
 			kfree(pages);
 			ret |= VM_FAULT_OOM;
 			goto out;


> 
> 
> >  			kfree(pages);
> >  			ret |= VM_FAULT_OOM;
> >  			goto out;
> > @@ -455,8 +467,10 @@ out:
> >  
> >  out_free_pages:
> >  	spin_unlock(&mm->page_table_lock);
> > -	for (i = 0; i < HPAGE_PMD_NR; i++)
> > +	for (i = 0; i < HPAGE_PMD_NR; i++) {
> > +		mem_cgroup_uncharge_page(pages[i]);
> >  		put_page(pages[i]);
> > +	}
> 
> here, too.

This is actually a very unlikely path handling a thread race
condition, but I'll add it any way.

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -469,10 +469,12 @@ out:
 
 out_free_pages:
 	spin_unlock(&mm->page_table_lock);
+	mem_cgroup_uncharge_start();
 	for (i = 0; i < HPAGE_PMD_NR; i++) {
 		mem_cgroup_uncharge_page(pages[i]);
 		put_page(pages[i]);
 	}
+	mem_cgroup_uncharge_end();
 	kfree(pages);
 	goto out;
 }


> Hmm...it seems there are no codes for move_account() hugepage in series.
> I think it needs some complicated work to walk page table.

Agreed.
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