On Mon 07-01-19 15:21:10, Dan Williams wrote: [...] Thanks a lot for the additional information. And...
> Introduce shuffle_free_memory(), and its helper shuffle_zone(), to > perform a Fisher-Yates shuffle of the page allocator 'free_area' lists > when they are initially populated with free memory at boot and at > hotplug time. Do this based on either the presence of a > page_alloc.shuffle=Y command line parameter, or autodetection of a > memory-side-cache (to be added in a follow-on patch). ... to make it opt-in and also provide an opt-out to override for the auto-detected case. > The shuffling is done in terms of CONFIG_SHUFFLE_PAGE_ORDER sized free > pages where the default CONFIG_SHUFFLE_PAGE_ORDER is MAX_ORDER-1 i.e. > 10, 4MB this trades off randomization granularity for time spent > shuffling. But I do not really think we want to make this a config option. Who do you expect will tune this? I would rather wait for those usecases to be called out and we can give them a command line parameter to do so rather than something hardcoded during compile time and as such really unusable for any consumer of the pre-built kernels. I do not have a problem with the default section though. > MAX_ORDER-1 was chosen to be minimally invasive to the page > allocator while still showing memory-side cache behavior improvements, > and the expectation that the security implications of finer granularity > randomization is mitigated by CONFIG_SLAB_FREELIST_RANDOM. > > The performance impact of the shuffling appears to be in the noise > compared to other memory initialization work. Also the bulk of the work > is done in the background as a part of deferred_init_memmap(). > > This initial randomization can be undone over time so a follow-on patch > is introduced to inject entropy on page free decisions. It is reasonable > to ask if the page free entropy is sufficient, but it is not enough due > to the in-order initial freeing of pages. At the start of that process > putting page1 in front or behind page0 still keeps them close together, > page2 is still near page1 and has a high chance of being adjacent. As > more pages are added ordering diversity improves, but there is still > high page locality for the low address pages and this leads to no > significant impact to the cache conflict rate. > > [1]: > https://itpeernetwork.intel.com/intel-optane-dc-persistent-memory-operating-modes/ > [2]: https://lkml.org/lkml/2018/9/22/54 > [3]: https://lkml.org/lkml/2018/10/12/309 Please turn lkml.org links into http://lkml.kernel.org/r/$msg_id [....] > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index cc4a507d7ca4..8c37a023a790 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1272,6 +1272,10 @@ void sparse_init(void); > #else > #define sparse_init() do {} while (0) > #define sparse_index_init(_sec, _nid) do {} while (0) > +static inline int pfn_present(unsigned long pfn) > +{ > + return 1; > +} Does this really make sense? Shouldn't this default to pfn_valid on !sparsemem? [...] > +config SHUFFLE_PAGE_ALLOCATOR > + bool "Page allocator randomization" > + depends on ACPI_NUMA > + default SLAB_FREELIST_RANDOM > + help > + Randomization of the page allocator improves the average > + utilization of a direct-mapped memory-side-cache. See section > + 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI > + 6.2a specification for an example of how a platform advertises > + the presence of a memory-side-cache. There are also incidental > + security benefits as it reduces the predictability of page > + allocations to compliment SLAB_FREELIST_RANDOM, but the > + default granularity of shuffling on 4MB (MAX_ORDER) pages is > + selected based on cache utilization benefits. > + > + While the randomization improves cache utilization it may > + negatively impact workloads on platforms without a cache. For > + this reason, by default, the randomization is enabled only > + after runtime detection of a direct-mapped memory-side-cache. > + Otherwise, the randomization may be force enabled with the > + 'page_alloc.shuffle' kernel command line parameter. > + > + Say Y if unsure. Do we really need to make this a choice? Are any of the tiny systems going to be NUMA? Why cannot we just make it depend on ACPI_NUMA? > +config SHUFFLE_PAGE_ORDER > + depends on SHUFFLE_PAGE_ALLOCATOR > + int "Page allocator shuffle order" > + range 0 10 > + default 10 > + help > + Specify the granularity at which shuffling (randomization) is > + performed. By default this is set to MAX_ORDER-1 to minimize > + runtime impact of randomization and with the expectation that > + SLAB_FREELIST_RANDOM mitigates heap attacks on smaller > + object granularities. > + and no, do not make this configurable here as already mentioned. > diff --git a/mm/memblock.c b/mm/memblock.c > index 022d4cbb3618..3602f7a2eab4 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -17,6 +17,7 @@ > #include <linux/poison.h> > #include <linux/pfn.h> > #include <linux/debugfs.h> > +#include <linux/shuffle.h> > #include <linux/kmemleak.h> > #include <linux/seq_file.h> > #include <linux/memblock.h> > @@ -1929,9 +1930,16 @@ static unsigned long __init > free_low_memory_core_early(void) > * low ram will be on Node1 > */ > for_each_free_mem_range(i, NUMA_NO_NODE, MEMBLOCK_NONE, &start, &end, > - NULL) > + NULL) { > + pg_data_t *pgdat; > + > count += __free_memory_core(start, end); > > + for_each_online_pgdat(pgdat) > + shuffle_free_memory(pgdat, PHYS_PFN(start), > + PHYS_PFN(end)); > + } > + > return count; > } > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index b9a667d36c55..7caffb9a91ab 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -23,6 +23,7 @@ > #include <linux/highmem.h> > #include <linux/vmalloc.h> > #include <linux/ioport.h> > +#include <linux/shuffle.h> > #include <linux/delay.h> > #include <linux/migrate.h> > #include <linux/page-isolation.h> > @@ -895,6 +896,8 @@ int __ref online_pages(unsigned long pfn, unsigned long > nr_pages, int online_typ > zone->zone_pgdat->node_present_pages += onlined_pages; > pgdat_resize_unlock(zone->zone_pgdat, &flags); > > + shuffle_zone(zone, pfn, zone_end_pfn(zone)); > + > if (onlined_pages) { > node_states_set_node(nid, &arg); > if (need_zonelists_rebuild) > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index cde5dac6229a..2adcd6da8a07 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -61,6 +61,7 @@ > #include <linux/sched/rt.h> > #include <linux/sched/mm.h> > #include <linux/page_owner.h> > +#include <linux/shuffle.h> > #include <linux/kthread.h> > #include <linux/memcontrol.h> > #include <linux/ftrace.h> > @@ -1634,6 +1635,8 @@ static int __init deferred_init_memmap(void *data) > } > pgdat_resize_unlock(pgdat, &flags); > > + shuffle_zone(zone, first_init_pfn, zone_end_pfn(zone)); > + > /* Sanity check that the next zone really is unpopulated */ > WARN_ON(++zid < MAX_NR_ZONES && populated_zone(++zone)); I would prefer if would have less placess to place the shuffling. Why cannot we have a single place for the bootup and one for onlining part? page_alloc_init_late sounds like a good place for the later. You can miss some early allocations but are those of a big interest? I haven't checked the actual shuffling algorithm, I will trust you on that part ;) -- Michal Hocko SUSE Labs
