[Devel] Re: [PATCH 6/7] BC: kernel memory (core)

[Balbir Singh]

Kirill Korotaev wrote:
> Introduce BC_KMEMSIZE resource which accounts kernel
> objects allocated by task's request.
> 
> Reference to BC is kept on struct page or slab object.
> For slabs each struct slab contains a set of pointers
> corresponding objects are charged to.
> 
> Allocation charge rules:
> 1. Pages - if allocation is performed with __GFP_BC flag - page
>    is charged to current's exec_bc.
> 2. Slabs - kmem_cache may be created with SLAB_BC flag - in this
>    case each allocation is charged. Caches used by kmalloc are
>    created with SLAB_BC | SLAB_BC_NOCHARGE flags. In this case
>    only __GFP_BC allocations are charged.
> 

<snip>

> +#define __GFP_BC_LIMIT ((__force gfp_t)0x100000u) /* Charge against BC 
> limit */
> 

What's _GFP_BC_LIMIT for, could you add the description for that flag?
The comment is not very clear

> +#ifdef CONFIG_BEANCOUNTERS
> +    union {
> +        struct beancounter    *page_bc;
> +    } bc;
> +#endif
> };
> 
> +#define page_bc(page)            ((page)->bc.page_bc)

Minor comment - page->(bc).page_bc has too many repititions of page and bc - see
the Practice of Programming by Kernighan and Pike

I missed the part of why you wanted to have a union (in struct page for bc)?

> const char *bc_rnames[] = {
> +    "kmemsize",    /* 0 */
> };
> 
> static struct hlist_head bc_hash[BC_HASH_SIZE];
> @@ -221,6 +222,8 @@ static void init_beancounter_syslimits(s
> { 
>     int k;
> 
> +    bc->bc_parms[BC_KMEMSIZE].limit = 32 * 1024 * 1024;
> +

Can't this be configurable CONFIG_XXX or a #defined constant?

> --- ./mm/mempool.c.bckmem    2006-04-21 11:59:36.000000000 +0400
> +++ ./mm/mempool.c    2006-08-28 12:59:28.000000000 +0400
> @@ -119,6 +119,7 @@ int mempool_resize(mempool_t *pool, int     unsigned 
> long flags;
> 
>     BUG_ON(new_min_nr <= 0);
> +    gfp_mask &= ~__GFP_BC;
> 
>     spin_lock_irqsave(&pool->lock, flags);
>     if (new_min_nr <= pool->min_nr) {
> @@ -212,6 +213,7 @@ void * mempool_alloc(mempool_t *pool, gf
>     gfp_mask |= __GFP_NOMEMALLOC;    /* don't allocate emergency 
> reserves */
>     gfp_mask |= __GFP_NORETRY;    /* don't loop in __alloc_pages */
>     gfp_mask |= __GFP_NOWARN;    /* failures are OK */
> +    gfp_mask &= ~__GFP_BC;        /* do not charge */
> 
>     gfp_temp = gfp_mask & ~(__GFP_WAIT|__GFP_IO);
>

Is there any reasn why mempool_xxxx() functions are not charged? Is it because
mempool functions are mostly used from the I/O path?

> --- ./mm/page_alloc.c.bckmem    2006-08-28 12:20:13.000000000 +0400
> +++ ./mm/page_alloc.c    2006-08-28 12:59:28.000000000 +0400
> @@ -40,6 +40,8 @@
> #include <linux/sort.h>
> #include <linux/pfn.h>
> 
> +#include <bc/kmem.h>
> +
> #include <asm/tlbflush.h>
> #include <asm/div64.h>
> #include "internal.h"
> @@ -516,6 +518,8 @@ static void __free_pages_ok(struct page     if 
> (reserved)
>         return;
> 
> +    bc_page_uncharge(page, order);
> +
>     kernel_map_pages(page, 1 << order, 0);
>     local_irq_save(flags);
>     __count_vm_events(PGFREE, 1 << order);
> @@ -799,6 +803,8 @@ static void fastcall free_hot_cold_page(
>     if (free_pages_check(page))
>         return;
> 
> +    bc_page_uncharge(page, 0);
> +
>     kernel_map_pages(page, 1, 0);
> 
>     pcp = &zone_pcp(zone, get_cpu())->pcp[cold];
> @@ -1188,6 +1194,11 @@ nopage:
>         show_mem();
>     }
> got_pg:
> +    if ((gfp_mask & __GFP_BC) &&
> +            bc_page_charge(page, order, gfp_mask)) {

I wonder if bc_page_charge() should be called bc_page_charge_failed()?
Does it make sense to atleast partially start reclamation here? I know with
bean counters we cannot reclaim from a particular container, but for now
we could kick off kswapd() or call shrink_all_memory() inline (Dave's patches do 
this to shrink memory from the particular cpuset). Or do you want to leave this
slot open for later?

> +        __free_pages(page, order);
> +        page = NULL;
> +    }


-- 

	Balbir Singh,
	Linux Technology Center,
	IBM Software Labs