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Date: Mon, 19 Sep 2011 14:53:33 +0200
From: Michal Hocko <mhocko@...e.cz>
To: Johannes Weiner <jweiner@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
Balbir Singh <bsingharora@...il.com>,
Ying Han <yinghan@...gle.com>,
Greg Thelen <gthelen@...gle.com>,
Michel Lespinasse <walken@...gle.com>,
Rik van Riel <riel@...hat.com>,
Minchan Kim <minchan.kim@...il.com>,
Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [patch 01/11] mm: memcg: consolidate hierarchy iteration
primitives
Hi,
On Mon 12-09-11 12:57:18, Johannes Weiner wrote:
> Memory control groups are currently bolted onto the side of
> traditional memory management in places where better integration would
> be preferrable. To reclaim memory, for example, memory control groups
> maintain their own LRU list and reclaim strategy aside from the global
> per-zone LRU list reclaim. But an extra list head for each existing
> page frame is expensive and maintaining it requires additional code.
>
> This patchset disables the global per-zone LRU lists on memory cgroup
> configurations and converts all its users to operate on the per-memory
> cgroup lists instead. As LRU pages are then exclusively on one list,
> this saves two list pointers for each page frame in the system:
>
> page_cgroup array size with 4G physical memory
>
> vanilla: [ 0.000000] allocated 31457280 bytes of page_cgroup
> patched: [ 0.000000] allocated 15728640 bytes of page_cgroup
>
> At the same time, system performance for various workloads is
> unaffected:
>
> 100G sparse file cat, 4G physical memory, 10 runs, to test for code
> bloat in the traditional LRU handling and kswapd & direct reclaim
> paths, without/with the memory controller configured in
>
> vanilla: 71.603(0.207) seconds
> patched: 71.640(0.156) seconds
>
> vanilla: 79.558(0.288) seconds
> patched: 77.233(0.147) seconds
>
> 100G sparse file cat in 1G memory cgroup, 10 runs, to test for code
> bloat in the traditional memory cgroup LRU handling and reclaim path
>
> vanilla: 96.844(0.281) seconds
> patched: 94.454(0.311) seconds
>
> 4 unlimited memcgs running kbuild -j32 each, 4G physical memory, 500M
> swap on SSD, 10 runs, to test for regressions in kswapd & direct
> reclaim using per-memcg LRU lists with multiple memcgs and multiple
> allocators within each memcg
>
> vanilla: 717.722(1.440) seconds [ 69720.100(11600.835) majfaults ]
> patched: 714.106(2.313) seconds [ 71109.300(14886.186) majfaults ]
>
> 16 unlimited memcgs running kbuild, 1900M hierarchical limit, 500M
> swap on SSD, 10 runs, to test for regressions in hierarchical memcg
> setups
>
> vanilla: 2742.058(1.992) seconds [ 26479.600(1736.737) majfaults ]
> patched: 2743.267(1.214) seconds [ 27240.700(1076.063) majfaults ]
I guess you want to have this in the first patch to have it for
reference once it gets to the tree, right? I have no objections but it
seems unrelated to the patch and so it might be confusing a bit. I
haven't seen other patches in the series so there is probably no better
place to put this.
>
> This patch:
>
> There are currently two different implementations of iterating over a
> memory cgroup hierarchy tree.
>
> Consolidate them into one worker function and base the convenience
> looping-macros on top of it.
>
> Signed-off-by: Johannes Weiner <jweiner@...hat.com>
Looks mostly good. There is just one issue I spotted and I guess we
want some comments. After the issue is fixed:
Reviewed-by: Michal Hocko <mhocko@...e.cz>
> ---
> mm/memcontrol.c | 196 ++++++++++++++++++++----------------------------------
> 1 files changed, 73 insertions(+), 123 deletions(-)
Nice diet.
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b76011a..912c7c7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -781,83 +781,75 @@ struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
> return memcg;
> }
>
> -/* The caller has to guarantee "mem" exists before calling this */
Shouldn't we have a similar comment that we have to keep a reference to
root if non-NULL. A mention about remember parameter and what is it used
for (hierarchical reclaim) would be helpful as well.
/*
* Find a next cgroup under the hierarchy tree with the given root (or
* root_mem_cgroup if NULL) starting from the given prev (iterator)
* position and releasing a reference to it. Start from the root if
* iterator is NULL.
* Ignore iterator position if remember is true and follow with the
* last_scanned_child instead and remember the new value (used during
* hierarchical reclaim).
* Caller is supposed to grab a reference to the root (if non NULL) before
* it calls us for the first time.
*
* Returns a cgroup with increased reference count (except for the root)
* or NULL if there are no more groups to visit.
*
* Use for_each_mem_cgroup_tree and for_each_mem_cgroup instead and
* mem_cgroup_iter_break for the final clean up if you are using this
* function directly.
*/
> -static struct mem_cgroup *mem_cgroup_start_loop(struct mem_cgroup *memcg)
> +static struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
> + struct mem_cgroup *prev,
> + bool remember)
[...]
> @@ -1656,7 +1611,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_memcg,
> unsigned long reclaim_options,
> unsigned long *total_scanned)
> {
> - struct mem_cgroup *victim;
> + struct mem_cgroup *victim = NULL;
> int ret, total = 0;
> int loop = 0;
> bool noswap = reclaim_options & MEM_CGROUP_RECLAIM_NOSWAP;
> @@ -1672,8 +1627,8 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_memcg,
> noswap = true;
>
> while (1) {
> - victim = mem_cgroup_select_victim(root_memcg);
> - if (victim == root_memcg) {
> + victim = mem_cgroup_iter(root_memcg, victim, true);
> + if (!victim) {
> loop++;
> /*
> * We are not draining per cpu cached charges during
> @@ -1689,10 +1644,8 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_memcg,
> * anything, it might because there are
> * no reclaimable pages under this hierarchy
> */
> - if (!check_soft || !total) {
> - css_put(&victim->css);
> + if (!check_soft || !total)
> break;
> - }
> /*
> * We want to do more targeted reclaim.
> * excess >> 2 is not to excessive so as to
> @@ -1700,15 +1653,13 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_memcg,
> * coming back to reclaim from this cgroup
> */
> if (total >= (excess >> 2) ||
> - (loop > MEM_CGROUP_MAX_RECLAIM_LOOPS)) {
> - css_put(&victim->css);
> + (loop > MEM_CGROUP_MAX_RECLAIM_LOOPS))
> break;
> - }
> }
> + continue;
> }
> if (!mem_cgroup_reclaimable(victim, noswap)) {
> /* this cgroup's local usage == 0 */
> - css_put(&victim->css);
> continue;
> }
> /* we use swappiness of local cgroup */
> @@ -1719,21 +1670,21 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_memcg,
> } else
> ret = try_to_free_mem_cgroup_pages(victim, gfp_mask,
> noswap);
> - css_put(&victim->css);
> /*
> * At shrinking usage, we can't check we should stop here or
> * reclaim more. It's depends on callers. last_scanned_child
> * will work enough for keeping fairness under tree.
> */
> if (shrink)
> - return ret;
> + break;
Hmm, we are returning total but it doesn't get set to ret for shrinking
case so we are alway returning 0. You want to move the line bellow up.
> total += ret;
> if (check_soft) {
> if (!res_counter_soft_limit_excess(&root_memcg->res))
> - return total;
> + break;
> } else if (mem_cgroup_margin(root_memcg))
> - return total;
> + break;
> }
> + mem_cgroup_iter_break(root_memcg, victim);
> return total;
> }
[...]
Thanks
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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