From: Michal Hocko <mhocko@kernel.org>
To: Mel Gorman <mgorman@suse.de>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Vlastimil Babka <vbabka@suse.cz>,
LKML <linux-kernel@vger.kernel.org>,
linux-api@vger.kernel.org
Subject: Re: [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE
Date: Fri, 14 Jul 2017 12:47:57 +0200 [thread overview]
Message-ID: <20170714104756.GD2618@dhcp22.suse.cz> (raw)
In-Reply-To: <20170714093650.l67vbem2g4typkta@suse.de>
On Fri 14-07-17 10:36:50, Mel Gorman wrote:
> On Fri, Jul 14, 2017 at 09:59:58AM +0200, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@suse.com>
> >
> > Supporting zone ordered zonelists costs us just a lot of code while
> > the usefulness is arguable if existent at all. Mel has already made
> > node ordering default on 64b systems. 32b systems are still using
> > ZONELIST_ORDER_ZONE because it is considered better to fallback to
> > a different NUMA node rather than consume precious lowmem zones.
> >
> > This argument is, however, weaken by the fact that the memory reclaim
> > has been reworked to be node rather than zone oriented. This means
> > that lowmem requests have to skip over all highmem pages on LRUs already
> > and so zone ordering doesn't save the reclaim time much. So the only
> > advantage of the zone ordering is under a light memory pressure when
> > highmem requests do not ever hit into lowmem zones and the lowmem
> > pressure doesn't need to reclaim.
> >
> > Considering that 32b NUMA systems are rather suboptimal already and
> > it is generally advisable to use 64b kernel on such a HW I believe we
> > should rather care about the code maintainability and just get rid of
> > ZONELIST_ORDER_ZONE altogether. Keep systcl in place and warn if
> > somebody tries to set zone ordering either from kernel command line
> > or the sysctl.
> >
> > Cc: <linux-api@vger.kernel.org>
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > index 80e4adb4c360..d9f4ea057e74 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4864,40 +4824,22 @@ int numa_zonelist_order_handler(struct ctl_table *table, int write,
> > void __user *buffer, size_t *length,
> > loff_t *ppos)
> > {
> > - char saved_string[NUMA_ZONELIST_ORDER_LEN];
> > + char *str;
> > int ret;
> > - static DEFINE_MUTEX(zl_order_mutex);
> >
> > - mutex_lock(&zl_order_mutex);
> > - if (write) {
> > - if (strlen((char *)table->data) >= NUMA_ZONELIST_ORDER_LEN) {
> > - ret = -EINVAL;
> > - goto out;
> > - }
> > - strcpy(saved_string, (char *)table->data);
> > + if (!write) {
> > + int len = sizeof("Default");
> > + if (copy_to_user(buffer, "Default", len))
> > + return -EFAULT;
> > + return len;
> > }
>
> That should to be "default" because the original code would have the proc
> entry display "default" unless it was set at runtime. Pretty weird I
> know but it's always possible someone is parsing the original default
> and not handling it properly.
Ohh, right! That is indeed strange. Then I guess it would be probably
better to simply return Node to make it clear what the default is. What
do you think?
> Otherwise I think we're way past the point where large memory 32-bit
> NUMA machines are a thing so
>
> Acked-by: Mel Gorman <mgorman@suse.de>
Thanks!
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-07-14 10:47 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-14 7:59 [PATCH 0/9] cleanup zonelists initialization Michal Hocko
2017-07-14 7:59 ` [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE Michal Hocko
[not found] ` <20170714080006.7250-2-mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2017-07-14 9:36 ` Mel Gorman
2017-07-14 10:47 ` Michal Hocko [this message]
[not found] ` <20170714104756.GD2618-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>
2017-07-14 11:16 ` Mel Gorman
2017-07-14 11:38 ` Michal Hocko
2017-07-14 12:56 ` Mel Gorman
[not found] ` <20170714125616.clbp4ezgtoon6cmk-l3A5Bk7waGM@public.gmane.org>
2017-07-14 13:01 ` Mel Gorman
2017-07-14 13:08 ` Michal Hocko
2017-07-19 9:33 ` Vlastimil Babka
[not found] ` <a4490c3e-9f7b-72b2-dfa3-80c054df6600-AlSwsSmVLrQ@public.gmane.org>
2017-07-19 13:44 ` Michal Hocko
[not found] <20170721143915.14161-1-mhocko@kernel.org>
[not found] ` <20170721143915.14161-2-mhocko@kernel.org>
2017-07-21 14:45 ` Michal Hocko
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