| Message ID | 20190617043635.13201-5-alastair@au1.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: Cleanup & allow modules to hotplug memory | expand |
On Mon, Jun 17, 2019 at 02:36:30PM +1000, Alastair D'Silva wrote: > From: Alastair D'Silva <alastair@d-silva.org> > > When removing sufficiently large amounts of memory, we trigger RCU stall > detection. By periodically calling cond_resched(), we avoid bogus stall > warnings. > > Signed-off-by: Alastair D'Silva <alastair@d-silva.org> > --- > mm/memory_hotplug.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index e096c987d261..382b3a0c9333 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -578,6 +578,9 @@ void __remove_pages(struct zone *zone, unsigned long phys_start_pfn, > __remove_section(zone, __pfn_to_section(pfn), map_offset, > altmap); > map_offset = 0; > + > + if (!(i & 0x0FFF)) No magic numbers please. And a comment would be appreciated. > + cond_resched(); > } > > set_zone_contiguous(zone); > -- > 2.21.0 >
On Mon, 2019-06-17 at 09:53 +0300, Mike Rapoport wrote: > On Mon, Jun 17, 2019 at 02:36:30PM +1000, Alastair D'Silva wrote: > > From: Alastair D'Silva <alastair@d-silva.org> > > > > When removing sufficiently large amounts of memory, we trigger RCU > > stall > > detection. By periodically calling cond_resched(), we avoid bogus > > stall > > warnings. > > > > Signed-off-by: Alastair D'Silva <alastair@d-silva.org> > > --- > > mm/memory_hotplug.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > > index e096c987d261..382b3a0c9333 100644 > > --- a/mm/memory_hotplug.c > > +++ b/mm/memory_hotplug.c > > @@ -578,6 +578,9 @@ void __remove_pages(struct zone *zone, unsigned > > long phys_start_pfn, > > __remove_section(zone, __pfn_to_section(pfn), > > map_offset, > > altmap); > > map_offset = 0; > > + > > + if (!(i & 0x0FFF)) > > No magic numbers please. And a comment would be appreciated. > Agreed, thanks for the review.
On Mon 17-06-19 14:36:30, Alastair D'Silva wrote: > From: Alastair D'Silva <alastair@d-silva.org> > > When removing sufficiently large amounts of memory, we trigger RCU stall > detection. By periodically calling cond_resched(), we avoid bogus stall > warnings. > > Signed-off-by: Alastair D'Silva <alastair@d-silva.org> > --- > mm/memory_hotplug.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index e096c987d261..382b3a0c9333 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -578,6 +578,9 @@ void __remove_pages(struct zone *zone, unsigned long phys_start_pfn, > __remove_section(zone, __pfn_to_section(pfn), map_offset, > altmap); > map_offset = 0; > + > + if (!(i & 0x0FFF)) > + cond_resched(); We already do have cond_resched before __remove_section. Why is an additional needed? > } > > set_zone_contiguous(zone); > -- > 2.21.0 >
> -----Original Message----- > From: Michal Hocko <mhocko@kernel.org> > Sent: Monday, 17 June 2019 5:47 PM > To: Alastair D'Silva <alastair@au1.ibm.com> > Cc: alastair@d-silva.org; Arun KS <arunks@codeaurora.org>; Mukesh Ojha > <mojha@codeaurora.org>; Logan Gunthorpe <logang@deltatee.com>; Wei > Yang <richard.weiyang@gmail.com>; Peter Zijlstra <peterz@infradead.org>; > Ingo Molnar <mingo@kernel.org>; linux-mm@kvack.org; Qian Cai > <cai@lca.pw>; Thomas Gleixner <tglx@linutronix.de>; Andrew Morton > <akpm@linux-foundation.org>; Mike Rapoport <rppt@linux.vnet.ibm.com>; > Baoquan He <bhe@redhat.com>; David Hildenbrand <david@redhat.com>; > Josh Poimboeuf <jpoimboe@redhat.com>; Pavel Tatashin > <pasha.tatashin@soleen.com>; Juergen Gross <jgross@suse.com>; Oscar > Salvador <osalvador@suse.com>; Jiri Kosina <jkosina@suse.cz>; linux- > kernel@vger.kernel.org > Subject: Re: [PATCH 4/5] mm/hotplug: Avoid RCU stalls when removing large > amounts of memory > > On Mon 17-06-19 14:36:30, Alastair D'Silva wrote: > > From: Alastair D'Silva <alastair@d-silva.org> > > > > When removing sufficiently large amounts of memory, we trigger RCU > > stall detection. By periodically calling cond_resched(), we avoid > > bogus stall warnings. > > > > Signed-off-by: Alastair D'Silva <alastair@d-silva.org> > > --- > > mm/memory_hotplug.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index > > e096c987d261..382b3a0c9333 100644 > > --- a/mm/memory_hotplug.c > > +++ b/mm/memory_hotplug.c > > @@ -578,6 +578,9 @@ void __remove_pages(struct zone *zone, unsigned > long phys_start_pfn, > > __remove_section(zone, __pfn_to_section(pfn), > map_offset, > > altmap); > > map_offset = 0; > > + > > + if (!(i & 0x0FFF)) > > + cond_resched(); > > We already do have cond_resched before __remove_section. Why is an > additional needed? I was getting stalls when removing ~1TB of memory.
On Mon 17-06-19 17:57:16, Alastair D'Silva wrote: > > -----Original Message----- > > From: Michal Hocko <mhocko@kernel.org> > > Sent: Monday, 17 June 2019 5:47 PM > > To: Alastair D'Silva <alastair@au1.ibm.com> > > Cc: alastair@d-silva.org; Arun KS <arunks@codeaurora.org>; Mukesh Ojha > > <mojha@codeaurora.org>; Logan Gunthorpe <logang@deltatee.com>; Wei > > Yang <richard.weiyang@gmail.com>; Peter Zijlstra <peterz@infradead.org>; > > Ingo Molnar <mingo@kernel.org>; linux-mm@kvack.org; Qian Cai > > <cai@lca.pw>; Thomas Gleixner <tglx@linutronix.de>; Andrew Morton > > <akpm@linux-foundation.org>; Mike Rapoport <rppt@linux.vnet.ibm.com>; > > Baoquan He <bhe@redhat.com>; David Hildenbrand <david@redhat.com>; > > Josh Poimboeuf <jpoimboe@redhat.com>; Pavel Tatashin > > <pasha.tatashin@soleen.com>; Juergen Gross <jgross@suse.com>; Oscar > > Salvador <osalvador@suse.com>; Jiri Kosina <jkosina@suse.cz>; linux- > > kernel@vger.kernel.org > > Subject: Re: [PATCH 4/5] mm/hotplug: Avoid RCU stalls when removing large > > amounts of memory > > > > On Mon 17-06-19 14:36:30, Alastair D'Silva wrote: > > > From: Alastair D'Silva <alastair@d-silva.org> > > > > > > When removing sufficiently large amounts of memory, we trigger RCU > > > stall detection. By periodically calling cond_resched(), we avoid > > > bogus stall warnings. > > > > > > Signed-off-by: Alastair D'Silva <alastair@d-silva.org> > > > --- > > > mm/memory_hotplug.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index > > > e096c987d261..382b3a0c9333 100644 > > > --- a/mm/memory_hotplug.c > > > +++ b/mm/memory_hotplug.c > > > @@ -578,6 +578,9 @@ void __remove_pages(struct zone *zone, unsigned > > long phys_start_pfn, > > > __remove_section(zone, __pfn_to_section(pfn), > > map_offset, > > > altmap); > > > map_offset = 0; > > > + > > > + if (!(i & 0x0FFF)) > > > + cond_resched(); > > > > We already do have cond_resched before __remove_section. Why is an > > additional needed? > > I was getting stalls when removing ~1TB of memory. Have debugged what is the source of the stall? We do cond_resched once a memory section which should be a constant unit of work regardless of the total amount of memory to be removed.
On Mon, Jun 17, 2019 at 05:57:16PM +1000, Alastair D'Silva wrote:
> I was getting stalls when removing ~1TB of memory.
Would you mind sharing one of those stalls-splats?
I am bit spectic here because as I Michal pointed out, we do cond_resched
once per section removed.
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index e096c987d261..382b3a0c9333 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -578,6 +578,9 @@ void __remove_pages(struct zone *zone, unsigned long phys_start_pfn, __remove_section(zone, __pfn_to_section(pfn), map_offset, altmap); map_offset = 0; + + if (!(i & 0x0FFF)) + cond_resched(); } set_zone_contiguous(zone);