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Date: Thu, 4 Jun 2009 14:33:18 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: nishimura@....nes.nec.co.jp,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>
Subject: Re: [PATCH] remove memory.limit v.s. memsw.limit comparison.
On Thu, 4 Jun 2009 14:10:43 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> Removes memory.limit < memsw.limit at setting limit check completely.
>
> The limitation "memory.limit <= memsw.limit" was added just because
> it seems sane ...if memory.limit > memsw.limit, only memsw.limit works.
>
> But To implement this limitation, we needed to use private mutex and make
> the code a bit complated.
> As Nishimura pointed out, in real world, there are people who only want
> to use memsw.limit.
>
> Then, this patch removes the check. user-land library or middleware can check
> this in userland easily if this really concerns.
>
> And this is a good change to charge-and-reclaim.
>
> Now, memory.limit is always checked before memsw.limit
> and it may do swap-out. But, if memory.limit == memsw.limit, swap-out is
> finally no help and hits memsw.limit again. So, let's allow the condition
> memory.limit > memsw.limit. Then we can skip unnecesary swap-out.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
I welcome this change very much :)
Reviewed-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Thanks,
Daisuke Nishimura.
> ---
> Documentation/cgroups/memory.txt | 15 +++++++++++----
> mm/memcontrol.c | 33 +--------------------------------
> 2 files changed, 12 insertions(+), 36 deletions(-)
>
> Index: mmotm-2.6.30-Jun3/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.30-Jun3.orig/mm/memcontrol.c
> +++ mmotm-2.6.30-Jun3/mm/memcontrol.c
> @@ -1713,14 +1713,11 @@ int mem_cgroup_shmem_charge_fallback(str
> return ret;
> }
>
> -static DEFINE_MUTEX(set_limit_mutex);
> -
> static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
> unsigned long long val)
> {
> int retry_count;
> int progress;
> - u64 memswlimit;
> int ret = 0;
> int children = mem_cgroup_count_children(memcg);
> u64 curusage, oldusage;
> @@ -1739,20 +1736,7 @@ static int mem_cgroup_resize_limit(struc
> ret = -EINTR;
> break;
> }
> - /*
> - * Rather than hide all in some function, I do this in
> - * open coded manner. You see what this really does.
> - * We have to guarantee mem->res.limit < mem->memsw.limit.
> - */
> - mutex_lock(&set_limit_mutex);
> - memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
> - if (memswlimit < val) {
> - ret = -EINVAL;
> - mutex_unlock(&set_limit_mutex);
> - break;
> - }
> ret = res_counter_set_limit(&memcg->res, val);
> - mutex_unlock(&set_limit_mutex);
>
> if (!ret)
> break;
> @@ -1774,7 +1758,7 @@ static int mem_cgroup_resize_memsw_limit
> unsigned long long val)
> {
> int retry_count;
> - u64 memlimit, oldusage, curusage;
> + u64 oldusage, curusage;
> int children = mem_cgroup_count_children(memcg);
> int ret = -EBUSY;
>
> @@ -1786,24 +1770,9 @@ static int mem_cgroup_resize_memsw_limit
> ret = -EINTR;
> break;
> }
> - /*
> - * Rather than hide all in some function, I do this in
> - * open coded manner. You see what this really does.
> - * We have to guarantee mem->res.limit < mem->memsw.limit.
> - */
> - mutex_lock(&set_limit_mutex);
> - memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
> - if (memlimit > val) {
> - ret = -EINVAL;
> - mutex_unlock(&set_limit_mutex);
> - break;
> - }
> ret = res_counter_set_limit(&memcg->memsw, val);
> - mutex_unlock(&set_limit_mutex);
> -
> if (!ret)
> break;
> -
> mem_cgroup_hierarchical_reclaim(memcg, GFP_KERNEL, true, true);
> curusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
> /* Usage is reduced ? */
> Index: mmotm-2.6.30-Jun3/Documentation/cgroups/memory.txt
> ===================================================================
> --- mmotm-2.6.30-Jun3.orig/Documentation/cgroups/memory.txt
> +++ mmotm-2.6.30-Jun3/Documentation/cgroups/memory.txt
> @@ -155,11 +155,18 @@ usage of mem+swap is limited by memsw.li
> Note: why 'mem+swap' rather than swap.
> The global LRU(kswapd) can swap out arbitrary pages. Swap-out means
> to move account from memory to swap...there is no change in usage of
> -mem+swap.
> +mem+swap. In other words, when we want to limit the usage of swap
> +without affecting global LRU, mem+swap limit is better than just limiting
> +swap from OS point of view.
> +
> +
> +memory.limit v.s. memsw.limit
> +
> +There are no guarantee that memsw.limit is bigger than memory.limit
> +in the kernel. The user should notice what he really wants and use
> +proper size for limitation. Of course, if memsw.limit < memory.limit,
> +only memsw.limit works sane.
>
> -In other words, when we want to limit the usage of swap without affecting
> -global LRU, mem+swap limit is better than just limiting swap from OS point
> -of view.
>
> 2.5 Reclaim
>
>
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