Re: [RFC 4/4] Sparse initialization of struct page array.

Robin Holt
2013-07-25T02:25:45Z

On Fri, Jul 12, 2013 at 09:19:12PM -0700, Yinghai Lu wrote:
> On Thu, Jul 11, 2013 at 7:03 PM, Robin Holt <holt@sgi.com> wrote:
> > During boot of large memory machines, a significant portion of boot
> > is spent initializing the struct page array. The vast majority of
> > those pages are not referenced during boot.
> >
> > Change this over to only initializing the pages when they are
> > actually allocated.
> >
> > Besides the advantage of boot speed, this allows us the chance to
> > use normal performance monitoring tools to determine where the bulk
> > of time is spent during page initialization.
> >
> > Signed-off-by: Robin Holt <holt@sgi.com>
> > Signed-off-by: Nate Zimmer <nzimmer@sgi.com>
> > To: "H. Peter Anvin" <hpa@zytor.com>
> > To: Ingo Molnar <mingo@kernel.org>
> > Cc: Linux Kernel <linux-kernel@vger.kernel.org>
> > Cc: Linux MM <linux-mm@kvack.org>
> > Cc: Rob Landley <rob@landley.net>
> > Cc: Mike Travis <travis@sgi.com>
> > Cc: Daniel J Blueman <daniel@numascale-asia.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Greg KH <gregkh@linuxfoundation.org>
> > Cc: Yinghai Lu <yinghai@kernel.org>
> > Cc: Mel Gorman <mgorman@suse.de>
> > ---
> > include/linux/mm.h | 11 +++++
> > include/linux/page-flags.h | 5 +-
> > mm/nobootmem.c | 5 ++
> > mm/page_alloc.c | 117 +++++++++++++++++++++++++++++++++++++++++++--
> > 4 files changed, 132 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index e0c8528..3de08b5 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1330,8 +1330,19 @@ static inline void __free_reserved_page(struct page *page)
> > __free_page(page);
> > }
> >
> > +extern void __reserve_bootmem_region(phys_addr_t start, phys_addr_t end);
> > +
> > +static inline void __reserve_bootmem_page(struct page *page)
> > +{
> > + phys_addr_t start = page_to_pfn(page) << PAGE_SHIFT;
> > + phys_addr_t end = start + PAGE_SIZE;
> > +
> > + __reserve_bootmem_region(start, end);
> > +}
> > +
> > static inline void free_reserved_page(struct page *page)
> > {
> > + __reserve_bootmem_page(page);
> > __free_reserved_page(page);
> > adjust_managed_page_count(page, 1);
> > }
> > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > index 6d53675..79e8eb7 100644
> > --- a/include/linux/page-flags.h
> > +++ b/include/linux/page-flags.h
> > @@ -83,6 +83,7 @@ enum pageflags {
> > PG_owner_priv_1, /* Owner use. If pagecache, fs may use*/
> > PG_arch_1,
> > PG_reserved,
> > + PG_uninitialized2mib, /* Is this the right spot? ntz - Yes - rmh */
> > PG_private, /* If pagecache, has fs-private data */
> > PG_private_2, /* If pagecache, has fs aux data */
> > PG_writeback, /* Page is under writeback */
> > @@ -211,6 +212,8 @@ PAGEFLAG(SwapBacked, swapbacked) __CLEARPAGEFLAG(SwapBacked, swapbacked)
> >
> > __PAGEFLAG(SlobFree, slob_free)
> >
> > +PAGEFLAG(Uninitialized2Mib, uninitialized2mib)
> > +
> > /*
> > * Private page markings that may be used by the filesystem that owns the page
> > * for its own purposes.
> > @@ -499,7 +502,7 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
> > #define PAGE_FLAGS_CHECK_AT_FREE \
> > (1 << PG_lru | 1 << PG_locked | \
> > 1 << PG_private | 1 << PG_private_2 | \
> > - 1 << PG_writeback | 1 << PG_reserved | \
> > + 1 << PG_writeback | 1 << PG_reserved | 1 << PG_uninitialized2mib | \
> > 1 << PG_slab | 1 << PG_swapcache | 1 << PG_active | \
> > 1 << PG_unevictable | __PG_MLOCKED | __PG_HWPOISON | \
> > __PG_COMPOUND_LOCK)
> > diff --git a/mm/nobootmem.c b/mm/nobootmem.c
> > index 3b512ca..e3a386d 100644
> > --- a/mm/nobootmem.c
> > +++ b/mm/nobootmem.c
> > @@ -126,6 +126,9 @@ static unsigned long __init free_low_memory_core_early(void)
> > phys_addr_t start, end, size;
> > u64 i;
> >
> > + for_each_reserved_mem_region(i, &start, &end)
> > + __reserve_bootmem_region(start, end);
> > +
>
> How about holes that is not in memblock.reserved?
>
> before this patch:
> free_area_init_node/free_area_init_core/memmap_init_zone
> will mark all page in node range to Reserved in struct page, at first.
>
> but those holes is not mapped via kernel low mapping.
> so it should be ok not touch "struct page" for them.
>
> Now you only mark reserved for memblock.reserved at first, and later
> mark {memblock.memory} - { memblock.reserved} to be available.
> And that is ok.
>
> but should split that change to another patch and add some comment
> and change log for the change.
> in case there is some user like UEFI etc do weird thing.

Nate and I talked this over today. Sorry for the delay, but it was the
first time we were both free. Neither of us quite understands what you
are asking for here. My interpretation is that you would like us to
change the use of the PageReserved flag such that during boot, we do not
set the flag at all from memmap_init_zone, and then only set it on pages
which, at the time of free_all_bootmem, have been allocated/reserved in
the memblock allocator. Is that correct? I will start to work that up
on the assumption that is what you are asking for.

Robin

>
> > for_each_free_mem_range(i, MAX_NUMNODES, &start, &end, NULL)
> > count += __free_memory_core(start, end);
> >
> > @@ -162,6 +165,8 @@ unsigned long __init free_all_bootmem(void)
> > {
> > struct pglist_data *pgdat;
> >
> > + memblock_dump_all();
> > +
>
> Not needed.
>
> > for_each_online_pgdat(pgdat)
> > reset_node_lowmem_managed_pages(pgdat);
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 635b131..fe51eb9 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -740,6 +740,54 @@ static void __init_single_page(struct page *page, unsigned long zone, int nid, i
> > #endif
> > }
> >
> > +static void expand_page_initialization(struct page *basepage)
> > +{
> > + unsigned long pfn = page_to_pfn(basepage);
> > + unsigned long end_pfn = pfn + PTRS_PER_PMD;
> > + unsigned long zone = page_zonenum(basepage);
> > + int reserved = PageReserved(basepage);
> > + int nid = page_to_nid(basepage);
> > +
> > + ClearPageUninitialized2Mib(basepage);
> > +
> > + for( pfn++; pfn < end_pfn; pfn++ )
> > + __init_single_page(pfn_to_page(pfn), zone, nid, reserved);
> > +}
> > +
> > +void ensure_pages_are_initialized(unsigned long start_pfn,
> > + unsigned long end_pfn)
> > +{
> > + unsigned long aligned_start_pfn = start_pfn & ~(PTRS_PER_PMD - 1);
> > + unsigned long aligned_end_pfn;
> > + struct page *page;
> > +
> > + aligned_end_pfn = end_pfn & ~(PTRS_PER_PMD - 1);
> > + aligned_end_pfn += PTRS_PER_PMD;
> > + while (aligned_start_pfn < aligned_end_pfn) {
> > + if (pfn_valid(aligned_start_pfn)) {
> > + page = pfn_to_page(aligned_start_pfn);
> > +
> > + if(PageUninitialized2Mib(page))
> > + expand_page_initialization(page);
> > + }
> > +
> > + aligned_start_pfn += PTRS_PER_PMD;
> > + }
> > +}
> > +
> > +void __reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
> > +{
> > + unsigned long start_pfn = PFN_DOWN(start);
> > + unsigned long end_pfn = PFN_UP(end);
> > +
> > + ensure_pages_are_initialized(start_pfn, end_pfn);
> > +}
>
> that name is confusing, actually it is setting to struct page to Reserved only.
> maybe __reserve_pages_bootmem() to be aligned to free_pages_bootmem ?
>
> > +
> > +static inline void ensure_page_is_initialized(struct page *page)
> > +{
> > + __reserve_bootmem_page(page);
> > +}
>
> how about use __reserve_page_bootmem directly and add comment in callers site ?
>
> > +
> > static bool free_pages_prepare(struct page *page, unsigned int order)
> > {
> > int i;
> > @@ -751,7 +799,10 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
> > if (PageAnon(page))
> > page->mapping = NULL;
> > for (i = 0; i < (1 << order); i++)
> > - bad += free_pages_check(page + i);
> > + if (PageUninitialized2Mib(page + i))
> > + i += PTRS_PER_PMD - 1;
> > + else
> > + bad += free_pages_check(page + i);
> > if (bad)
> > return false;
> >
> > @@ -795,13 +846,22 @@ void __meminit __free_pages_bootmem(struct page *page, unsigned int order)
> > unsigned int loop;
> >
> > prefetchw(page);
> > - for (loop = 0; loop < nr_pages; loop++) {
> > + for (loop = 0; loop < nr_pages; ) {
> > struct page *p = &page[loop];
> >
> > if (loop + 1 < nr_pages)
> > prefetchw(p + 1);
> > +
> > + if ((PageUninitialized2Mib(p)) &&
> > + ((loop + PTRS_PER_PMD) > nr_pages))
> > + ensure_page_is_initialized(p);
> > +
> > __ClearPageReserved(p);
> > set_page_count(p, 0);
> > + if (PageUninitialized2Mib(p))
> > + loop += PTRS_PER_PMD;
> > + else
> > + loop += 1;
> > }
> >
> > page_zone(page)->managed_pages += 1 << order;
> > @@ -856,6 +916,7 @@ static inline void expand(struct zone *zone, struct page *page,
> > area--;
> > high--;
> > size >>= 1;
> > + ensure_page_is_initialized(page);
> > VM_BUG_ON(bad_range(zone, &page[size]));
> >
> > #ifdef CONFIG_DEBUG_PAGEALLOC
> > @@ -903,6 +964,10 @@ static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
> >
> > for (i = 0; i < (1 << order); i++) {
> > struct page *p = page + i;
> > +
> > + if (PageUninitialized2Mib(p))
> > + expand_page_initialization(page);
> > +
> > if (unlikely(check_new_page(p)))
> > return 1;
> > }
> > @@ -985,6 +1050,7 @@ int move_freepages(struct zone *zone,
> > unsigned long order;
> > int pages_moved = 0;
> >
> > + ensure_pages_are_initialized(page_to_pfn(start_page), page_to_pfn(end_page));
> > #ifndef CONFIG_HOLES_IN_ZONE
> > /*
> > * page_zone is not safe to call in this context when
> > @@ -3859,6 +3925,9 @@ static int pageblock_is_reserved(unsigned long start_pfn, unsigned long end_pfn)
> > for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> > if (!pfn_valid_within(pfn) || PageReserved(pfn_to_page(pfn)))
> > return 1;
> > +
> > + if (PageUninitialized2Mib(pfn_to_page(pfn)))
> > + pfn += PTRS_PER_PMD;
> > }
> > return 0;
> > }
> > @@ -3947,6 +4016,29 @@ static void setup_zone_migrate_reserve(struct zone *zone)
> > }
> > }
> >
> > +int __meminit pfn_range_init_avail(unsigned long pfn, unsigned long end_pfn,
> > + unsigned long size, int nid)
> why not use static ? it seems there is not outside user.
> > +{
> > + unsigned long validate_end_pfn = pfn + size;
> > +
> > + if (pfn & (size - 1))
> > + return 1;
> > +
> > + if (pfn + size >= end_pfn)
> > + return 1;
> > +
> > + while (pfn < validate_end_pfn)
> > + {
> > + if (!early_pfn_valid(pfn))
> > + return 1;
> > + if (!early_pfn_in_nid(pfn, nid))
> > + return 1;
> > + pfn++;
> > + }
> > +
> > + return size;
> > +}
> > +
> > /*
> > * Initially all pages are reserved - free ones are freed
> > * up by free_all_bootmem() once the early boot process is
> > @@ -3964,20 +4056,34 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> > highest_memmap_pfn = end_pfn - 1;
> >
> > z = &NODE_DATA(nid)->node_zones[zone];
> > - for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> > + for (pfn = start_pfn; pfn < end_pfn; ) {
> > /*
> > * There can be holes in boot-time mem_map[]s
> > * handed to this function. They do not
> > * exist on hotplugged memory.
> > */
> > + int pfns = 1;
> > if (context == MEMMAP_EARLY) {
> > - if (!early_pfn_valid(pfn))
> > + if (!early_pfn_valid(pfn)) {
> > + pfn++;
> > continue;
> > - if (!early_pfn_in_nid(pfn, nid))
> > + }
> > + if (!early_pfn_in_nid(pfn, nid)) {
> > + pfn++;
> > continue;
> > + }
> > +
> > + pfns = pfn_range_init_avail(pfn, end_pfn,
> > + PTRS_PER_PMD, nid);
> > }
>
> maybe could update memmap_init_zone() only iterate {memblock.memory} -
> {memblock.reserved}, so you do need to check avail ....
>
> as memmap_init_zone do not need to handle holes to mark reserve for them.
>
> > +
> > page = pfn_to_page(pfn);
> > __init_single_page(page, zone, nid, 1);
> > +
> > + if (pfns > 1)
> > + SetPageUninitialized2Mib(page);
> > +
> > + pfn += pfns;
> > }
> > }
> >
> > @@ -6196,6 +6302,7 @@ static const struct trace_print_flags pageflag_names[] = {
> > {1UL << PG_owner_priv_1, "owner_priv_1" },
> > {1UL << PG_arch_1, "arch_1" },
> > {1UL << PG_reserved, "reserved" },
> > + {1UL << PG_uninitialized2mib, "Uninit_2MiB" },
>
> PG_uninitialized_2m ?
>
> > {1UL << PG_private, "private" },
> > {1UL << PG_private_2, "private_2" },
> > {1UL << PG_writeback, "writeback" },
>
> Yinghai