* Re: [PATCH] mm: memcg/slab: optimize objcg stock draining
2021-01-06 4:22 [PATCH] mm: memcg/slab: optimize objcg stock draining Roman Gushchin
@ 2021-01-06 6:05 ` Shakeel Butt
2021-01-06 16:42 ` Roman Gushchin
2021-01-06 6:19 ` Imran Khan
` (2 subsequent siblings)
3 siblings, 1 reply; 7+ messages in thread
From: Shakeel Butt @ 2021-01-06 6:05 UTC (permalink / raw)
To: Roman Gushchin
Cc: Andrew Morton, Linux MM, Michal Hocko, Johannes Weiner, LKML,
Kernel Team, Imran Khan
On Tue, Jan 5, 2021 at 8:22 PM Roman Gushchin <guro@fb.com> wrote:
>
> Imran Khan reported a regression in hackbench results caused by the
> commit f2fe7b09a52b ("mm: memcg/slab: charge individual slab objects
> instead of pages"). The regression is noticeable in the case of
> a consequent allocation of several relatively large slab objects,
> e.g. skb's. As soon as the amount of stocked bytes exceeds PAGE_SIZE,
> drain_obj_stock() and __memcg_kmem_uncharge() are called, and it leads
> to a number of atomic operations in page_counter_uncharge().
>
> The corresponding call graph is below (provided by Imran Khan):
> |__alloc_skb
> | |
> | |__kmalloc_reserve.isra.61
> | | |
> | | |__kmalloc_node_track_caller
> | | | |
> | | | |slab_pre_alloc_hook.constprop.88
> | | | obj_cgroup_charge
> | | | | |
> | | | | |__memcg_kmem_charge
> | | | | | |
> | | | | | |page_counter_try_charge
> | | | | |
> | | | | |refill_obj_stock
> | | | | | |
> | | | | | |drain_obj_stock.isra.68
> | | | | | | |
> | | | | | | |__memcg_kmem_uncharge
> | | | | | | | |
> | | | | | | | |page_counter_uncharge
> | | | | | | | | |
> | | | | | | | | |page_counter_cancel
> | | | |
> | | | |
> | | | |__slab_alloc
> | | | | |
> | | | | |___slab_alloc
> | | | | |
> | | | |slab_post_alloc_hook
>
> Instead of directly uncharging the accounted kernel memory, it's
> possible to refill the generic page-sized per-cpu stock instead.
> It's a much faster operation, especially on a default hierarchy.
> As a bonus, __memcg_kmem_uncharge_page() will also get faster,
> so the freeing of page-sized kernel allocations (e.g. large kmallocs)
> will become faster.
>
> A similar change has been done earlier for the socket memory by
> the commit 475d0487a2ad ("mm: memcontrol: use per-cpu stocks for
> socket memory uncharging").
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Reported-by: Imran Khan <imran.f.khan@oracle.com>
I remember seeing this somewhere
https://lore.kernel.org/linux-mm/20190423154405.259178-1-shakeelb@google.com/
Reviewed-by: Shakeel Butt <shakeelb@google.com>
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: memcg/slab: optimize objcg stock draining
2021-01-06 6:05 ` Shakeel Butt
@ 2021-01-06 16:42 ` Roman Gushchin
0 siblings, 0 replies; 7+ messages in thread
From: Roman Gushchin @ 2021-01-06 16:42 UTC (permalink / raw)
To: Shakeel Butt
Cc: Andrew Morton, Linux MM, Michal Hocko, Johannes Weiner, LKML,
Kernel Team, Imran Khan
On Tue, Jan 05, 2021 at 10:05:20PM -0800, Shakeel Butt wrote:
> On Tue, Jan 5, 2021 at 8:22 PM Roman Gushchin <guro@fb.com> wrote:
> >
> > Imran Khan reported a regression in hackbench results caused by the
> > commit f2fe7b09a52b ("mm: memcg/slab: charge individual slab objects
> > instead of pages"). The regression is noticeable in the case of
> > a consequent allocation of several relatively large slab objects,
> > e.g. skb's. As soon as the amount of stocked bytes exceeds PAGE_SIZE,
> > drain_obj_stock() and __memcg_kmem_uncharge() are called, and it leads
> > to a number of atomic operations in page_counter_uncharge().
> >
> > The corresponding call graph is below (provided by Imran Khan):
> > |__alloc_skb
> > | |
> > | |__kmalloc_reserve.isra.61
> > | | |
> > | | |__kmalloc_node_track_caller
> > | | | |
> > | | | |slab_pre_alloc_hook.constprop.88
> > | | | obj_cgroup_charge
> > | | | | |
> > | | | | |__memcg_kmem_charge
> > | | | | | |
> > | | | | | |page_counter_try_charge
> > | | | | |
> > | | | | |refill_obj_stock
> > | | | | | |
> > | | | | | |drain_obj_stock.isra.68
> > | | | | | | |
> > | | | | | | |__memcg_kmem_uncharge
> > | | | | | | | |
> > | | | | | | | |page_counter_uncharge
> > | | | | | | | | |
> > | | | | | | | | |page_counter_cancel
> > | | | |
> > | | | |
> > | | | |__slab_alloc
> > | | | | |
> > | | | | |___slab_alloc
> > | | | | |
> > | | | |slab_post_alloc_hook
> >
> > Instead of directly uncharging the accounted kernel memory, it's
> > possible to refill the generic page-sized per-cpu stock instead.
> > It's a much faster operation, especially on a default hierarchy.
> > As a bonus, __memcg_kmem_uncharge_page() will also get faster,
> > so the freeing of page-sized kernel allocations (e.g. large kmallocs)
> > will become faster.
> >
> > A similar change has been done earlier for the socket memory by
> > the commit 475d0487a2ad ("mm: memcontrol: use per-cpu stocks for
> > socket memory uncharging").
> >
> > Signed-off-by: Roman Gushchin <guro@fb.com>
> > Reported-by: Imran Khan <imran.f.khan@oracle.com>
>
> I remember seeing this somewhere
> https://lore.kernel.org/linux-mm/20190423154405.259178-1-shakeelb@google.com/
Yes, we've discussed it a couple of times, as I remember. Looks like now
we finally have a good reasoning/benchmark, thanks to Imran.
>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>
Thank you for the review!
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm: memcg/slab: optimize objcg stock draining
2021-01-06 4:22 [PATCH] mm: memcg/slab: optimize objcg stock draining Roman Gushchin
2021-01-06 6:05 ` Shakeel Butt
@ 2021-01-06 6:19 ` Imran Khan
2021-01-06 19:50 ` Andrew Morton
2021-01-20 16:34 ` Michal Koutný
3 siblings, 0 replies; 7+ messages in thread
From: Imran Khan @ 2021-01-06 6:19 UTC (permalink / raw)
To: Roman Gushchin, Andrew Morton, linux-mm
Cc: Michal Hocko, Johannes Weiner, Shakeel Butt, linux-kernel, kernel-team
On 6/1/21 3:22 pm, Roman Gushchin wrote:
> Imran Khan reported a regression in hackbench results caused by the
> commit f2fe7b09a52b ("mm: memcg/slab: charge individual slab objects
> instead of pages"). The regression is noticeable in the case of
> a consequent allocation of several relatively large slab objects,
> e.g. skb's. As soon as the amount of stocked bytes exceeds PAGE_SIZE,
> drain_obj_stock() and __memcg_kmem_uncharge() are called, and it leads
> to a number of atomic operations in page_counter_uncharge().
>
> The corresponding call graph is below (provided by Imran Khan):
> |__alloc_skb
> | |
> | |__kmalloc_reserve.isra.61
> | | |
> | | |__kmalloc_node_track_caller
> | | | |
> | | | |slab_pre_alloc_hook.constprop.88
> | | | obj_cgroup_charge
> | | | | |
> | | | | |__memcg_kmem_charge
> | | | | | |
> | | | | | |page_counter_try_charge
> | | | | |
> | | | | |refill_obj_stock
> | | | | | |
> | | | | | |drain_obj_stock.isra.68
> | | | | | | |
> | | | | | | |__memcg_kmem_uncharge
> | | | | | | | |
> | | | | | | | |page_counter_uncharge
> | | | | | | | | |
> | | | | | | | | |page_counter_cancel
> | | | |
> | | | |
> | | | |__slab_alloc
> | | | | |
> | | | | |___slab_alloc
> | | | | |
> | | | |slab_post_alloc_hook
>
> Instead of directly uncharging the accounted kernel memory, it's
> possible to refill the generic page-sized per-cpu stock instead.
> It's a much faster operation, especially on a default hierarchy.
> As a bonus, __memcg_kmem_uncharge_page() will also get faster,
> so the freeing of page-sized kernel allocations (e.g. large kmallocs)
> will become faster.
>
> A similar change has been done earlier for the socket memory by
> the commit 475d0487a2ad ("mm: memcontrol: use per-cpu stocks for
> socket memory uncharging").
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Reported-by: Imran Khan <imran.f.khan@oracle.com>
Tested-by: Imran Khan <imran.f.khan@oracle.com>
> ---
> mm/memcontrol.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 0d74b80fa4de..8148c1df3aff 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3122,9 +3122,7 @@ void __memcg_kmem_uncharge(struct mem_cgroup *memcg, unsigned int nr_pages)
> if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
> page_counter_uncharge(&memcg->kmem, nr_pages);
>
> - page_counter_uncharge(&memcg->memory, nr_pages);
> - if (do_memsw_account())
> - page_counter_uncharge(&memcg->memsw, nr_pages);
> + refill_stock(memcg, nr_pages);
> }
>
> /**
>
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: memcg/slab: optimize objcg stock draining
2021-01-06 4:22 [PATCH] mm: memcg/slab: optimize objcg stock draining Roman Gushchin
2021-01-06 6:05 ` Shakeel Butt
2021-01-06 6:19 ` Imran Khan
@ 2021-01-06 19:50 ` Andrew Morton
2021-01-06 20:04 ` Roman Gushchin
2021-01-20 16:34 ` Michal Koutný
3 siblings, 1 reply; 7+ messages in thread
From: Andrew Morton @ 2021-01-06 19:50 UTC (permalink / raw)
To: Roman Gushchin
Cc: linux-mm, Michal Hocko, Johannes Weiner, Shakeel Butt,
linux-kernel, kernel-team, Imran Khan
On Tue, 5 Jan 2021 20:22:39 -0800 Roman Gushchin <guro@fb.com> wrote:
> Imran Khan reported a regression in hackbench results caused by the
> commit f2fe7b09a52b ("mm: memcg/slab: charge individual slab objects
> instead of pages").
How large was the regression?
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3122,9 +3122,7 @@ void __memcg_kmem_uncharge(struct mem_cgroup *memcg, unsigned int nr_pages)
> if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
> page_counter_uncharge(&memcg->kmem, nr_pages);
>
> - page_counter_uncharge(&memcg->memory, nr_pages);
> - if (do_memsw_account())
> - page_counter_uncharge(&memcg->memsw, nr_pages);
> + refill_stock(memcg, nr_pages);
> }
IOW, which kernel version(s) should we be patching?
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: memcg/slab: optimize objcg stock draining
2021-01-06 19:50 ` Andrew Morton
@ 2021-01-06 20:04 ` Roman Gushchin
0 siblings, 0 replies; 7+ messages in thread
From: Roman Gushchin @ 2021-01-06 20:04 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-mm, Michal Hocko, Johannes Weiner, Shakeel Butt,
linux-kernel, kernel-team, Imran Khan
On Wed, Jan 06, 2021 at 11:50:44AM -0800, Andrew Morton wrote:
> On Tue, 5 Jan 2021 20:22:39 -0800 Roman Gushchin <guro@fb.com> wrote:
>
> > Imran Khan reported a regression in hackbench results caused by the
> > commit f2fe7b09a52b ("mm: memcg/slab: charge individual slab objects
> > instead of pages").
>
> How large was the regression?
~16% according to Imran's data.
>
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -3122,9 +3122,7 @@ void __memcg_kmem_uncharge(struct mem_cgroup *memcg, unsigned int nr_pages)
> > if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
> > page_counter_uncharge(&memcg->kmem, nr_pages);
> >
> > - page_counter_uncharge(&memcg->memory, nr_pages);
> > - if (do_memsw_account())
> > - page_counter_uncharge(&memcg->memsw, nr_pages);
> > + refill_stock(memcg, nr_pages);
> > }
>
> IOW, which kernel version(s) should we be patching?
5.9+
Thanks!
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm: memcg/slab: optimize objcg stock draining
2021-01-06 4:22 [PATCH] mm: memcg/slab: optimize objcg stock draining Roman Gushchin
` (2 preceding siblings ...)
2021-01-06 19:50 ` Andrew Morton
@ 2021-01-20 16:34 ` Michal Koutný
3 siblings, 0 replies; 7+ messages in thread
From: Michal Koutný @ 2021-01-20 16:34 UTC (permalink / raw)
To: Roman Gushchin
Cc: Andrew Morton, linux-mm, Michal Hocko, Johannes Weiner,
Shakeel Butt, linux-kernel, kernel-team, Imran Khan
[-- Attachment #1: Type: text/plain, Size: 2286 bytes --]
On Tue, Jan 05, 2021 at 08:22:39PM -0800, Roman Gushchin <guro@fb.com> wrote:
> Imran Khan reported a regression in hackbench results caused by the
> commit f2fe7b09a52b ("mm: memcg/slab: charge individual slab objects
> instead of pages"). The regression is noticeable in the case of
> a consequent allocation of several relatively large slab objects,
> e.g. skb's. As soon as the amount of stocked bytes exceeds PAGE_SIZE,
> drain_obj_stock() and __memcg_kmem_uncharge() are called, and it leads
> to a number of atomic operations in page_counter_uncharge().
>
> The corresponding call graph is below (provided by Imran Khan):
> |__alloc_skb
> | |
> | |__kmalloc_reserve.isra.61
> | | |
> | | |__kmalloc_node_track_caller
> | | | |
> | | | |slab_pre_alloc_hook.constprop.88
> | | | obj_cgroup_charge
> | | | | |
> | | | | |__memcg_kmem_charge
> | | | | | |
> | | | | | |page_counter_try_charge
> | | | | |
> | | | | |refill_obj_stock
> | | | | | |
> | | | | | |drain_obj_stock.isra.68 <--- draining old memcg
> | | | | | | |
> | | | | | | |__memcg_kmem_uncharge
> | | | | | | | |
> | | | | | | | |page_counter_uncharge
> | | | | | | | | |
> | | | | | | | | |page_counter_cancel
> [...]
> - page_counter_uncharge(&memcg->memory, nr_pages);
> - if (do_memsw_account())
> - page_counter_uncharge(&memcg->memsw, nr_pages);
> + refill_stock(memcg, nr_pages);
I noticed that refill_stock(memcg,...) switches the local stock to
memcg.
In this particular call chain, the uncharged memcg is the old memcg of
stock->cached_objcg. The refill_stock() then may switch stock->cached to
the old memcg too. If the patch leads to better performance, then the
switch probably doesn't happen at this moment (and I guess
stock->cached_objcg and stock->cached can be independent to some extent,
so the old memcg in one needn't be the old in the latter).
In conclusion
Reviewed-by: Michal Koutný <mkoutny@suse.com>
Michal
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^ permalink raw reply [flat|nested] 7+ messages in thread