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SubjectRe: [PATCH v3 03/19] mm: memcg: convert vmstat slab counters to bytes
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On 5/20/20 9:26 PM, Roman Gushchin wrote:
> On Wed, May 20, 2020 at 02:25:22PM +0200, Vlastimil Babka wrote:
>>
>> However __mod_node_page_state() and mode_node_state() will now branch always. I
>> wonder if the "API clean" goal is worth it...
>
> You mean just adding a special write-side helper which will perform a conversion
> and put VM_WARN_ON_ONCE() into generic write-side helpers?

What I mean is that maybe node/global helpers should assume page granularity,
and lruvec/memcg helpers do the check is they should convert from bytes to pages
when calling node/global helpers. Then there would be no extra branches in
node/global helpers. But maybe it's not worth saving those branches, dunno.

>>
>> > --- a/mm/memcontrol.c
>> > +++ b/mm/memcontrol.c
>> > @@ -1409,9 +1409,8 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
>> > (u64)memcg_page_state(memcg, MEMCG_KERNEL_STACK_KB) *
>> > 1024);
>> > seq_buf_printf(&s, "slab %llu\n",
>> > - (u64)(memcg_page_state(memcg, NR_SLAB_RECLAIMABLE) +
>> > - memcg_page_state(memcg, NR_SLAB_UNRECLAIMABLE)) *
>> > - PAGE_SIZE);
>> > + (u64)(memcg_page_state(memcg, NR_SLAB_RECLAIMABLE_B) +
>> > + memcg_page_state(memcg, NR_SLAB_UNRECLAIMABLE_B)));
>> > seq_buf_printf(&s, "sock %llu\n",
>> > (u64)memcg_page_state(memcg, MEMCG_SOCK) *
>> > PAGE_SIZE);
>> > @@ -1445,11 +1444,9 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
>> > PAGE_SIZE);
>> >
>> > seq_buf_printf(&s, "slab_reclaimable %llu\n",
>> > - (u64)memcg_page_state(memcg, NR_SLAB_RECLAIMABLE) *
>> > - PAGE_SIZE);
>> > + (u64)memcg_page_state(memcg, NR_SLAB_RECLAIMABLE_B));
>> > seq_buf_printf(&s, "slab_unreclaimable %llu\n",
>> > - (u64)memcg_page_state(memcg, NR_SLAB_UNRECLAIMABLE) *
>> > - PAGE_SIZE);
>> > + (u64)memcg_page_state(memcg, NR_SLAB_UNRECLAIMABLE_B));
>>
>> So here we are now printing in bytes instead of pages, right? That's fine for
>> OOM report, but in sysfs aren't we breaking existing users?
>>
>
> Hm, but it was in bytes previously, look at that x * PAGE_SIZE.

Yeah, that's what I managed to overlook, sorry.

> Or do you mean that now it can be not rounded to PAGE_SIZE?
> If so, I don't think it breaks any expectations.
>
> Thanks!
>

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