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SubjectRe: [PATCH 3/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap
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Hi Alex,

Please re-base on linux-next, memmap_init_zone() has been updated there
compared to mainline. You might even find a way to unify some parts of
memmap_init_zone and memmap_init_zone_device as memmap_init_zone() is a
lot simpler now.

I think __init_single_page() should stay local to page_alloc.c to keep
the inlining optimization.

I will review you this patch once you send an updated version.

Thank you,
Pavel

On 9/10/18 7:43 PM, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@intel.com>
>
> The ZONE_DEVICE pages were being initialized in two locations. One was with
> the memory_hotplug lock held and another was outside of that lock. The
> problem with this is that it was nearly doubling the memory initialization
> time. Instead of doing this twice, once while holding a global lock and
> once without, I am opting to defer the initialization to the one outside of
> the lock. This allows us to avoid serializing the overhead for memory init
> and we can instead focus on per-node init times.
>
> One issue I encountered is that devm_memremap_pages and
> hmm_devmmem_pages_create were initializing only the pgmap field the same
> way. One wasn't initializing hmm_data, and the other was initializing it to
> a poison value. Since this is something that is exposed to the driver in
> the case of hmm I am opting for a third option and just initializing
> hmm_data to 0 since this is going to be exposed to unknown third party
> drivers.
>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
> ---
> include/linux/mm.h | 2 +
> kernel/memremap.c | 24 +++++---------
> mm/hmm.c | 12 ++++---
> mm/page_alloc.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++-
> 4 files changed, 105 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a61ebe8ad4ca..47b440bb3050 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -848,6 +848,8 @@ static inline bool is_zone_device_page(const struct page *page)
> {
> return page_zonenum(page) == ZONE_DEVICE;
> }
> +extern void memmap_init_zone_device(struct zone *, unsigned long,
> + unsigned long, struct dev_pagemap *);
> #else
> static inline bool is_zone_device_page(const struct page *page)
> {
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 5b8600d39931..d0c32e473f82 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -175,10 +175,10 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
> struct vmem_altmap *altmap = pgmap->altmap_valid ?
> &pgmap->altmap : NULL;
> struct resource *res = &pgmap->res;
> - unsigned long pfn, pgoff, order;
> + struct dev_pagemap *conflict_pgmap;
> pgprot_t pgprot = PAGE_KERNEL;
> + unsigned long pgoff, order;
> int error, nid, is_ram;
> - struct dev_pagemap *conflict_pgmap;
>
> align_start = res->start & ~(SECTION_SIZE - 1);
> align_size = ALIGN(res->start + resource_size(res), SECTION_SIZE)
> @@ -256,19 +256,13 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
> if (error)
> goto err_add_memory;
>
> - for_each_device_pfn(pfn, pgmap) {
> - struct page *page = pfn_to_page(pfn);
> -
> - /*
> - * ZONE_DEVICE pages union ->lru with a ->pgmap back
> - * pointer. It is a bug if a ZONE_DEVICE page is ever
> - * freed or placed on a driver-private list. Seed the
> - * storage with LIST_POISON* values.
> - */
> - list_del(&page->lru);
> - page->pgmap = pgmap;
> - percpu_ref_get(pgmap->ref);
> - }
> + /*
> + * Initialization of the pages has been deferred until now in order
> + * to allow us to do the work while not holding the hotplug lock.
> + */
> + memmap_init_zone_device(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
> + align_start >> PAGE_SHIFT,
> + align_size >> PAGE_SHIFT, pgmap);
>
> devm_add_action(dev, devm_memremap_pages_release, pgmap);
>
> diff --git a/mm/hmm.c b/mm/hmm.c
> index c968e49f7a0c..774d684fa2b4 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -1024,7 +1024,6 @@ static int hmm_devmem_pages_create(struct hmm_devmem *devmem)
> resource_size_t key, align_start, align_size, align_end;
> struct device *device = devmem->device;
> int ret, nid, is_ram;
> - unsigned long pfn;
>
> align_start = devmem->resource->start & ~(PA_SECTION_SIZE - 1);
> align_size = ALIGN(devmem->resource->start +
> @@ -1109,11 +1108,14 @@ static int hmm_devmem_pages_create(struct hmm_devmem *devmem)
> align_size >> PAGE_SHIFT, NULL);
> mem_hotplug_done();
>
> - for (pfn = devmem->pfn_first; pfn < devmem->pfn_last; pfn++) {
> - struct page *page = pfn_to_page(pfn);
> + /*
> + * Initialization of the pages has been deferred until now in order
> + * to allow us to do the work while not holding the hotplug lock.
> + */
> + memmap_init_zone_device(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
> + align_start >> PAGE_SHIFT,
> + align_size >> PAGE_SHIFT, &devmem->pagemap);
>
> - page->pgmap = &devmem->pagemap;
> - }
> return 0;
>
> error_add_memory:
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index a9b095a72fd9..81a3fd942c45 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5454,6 +5454,83 @@ void __ref build_all_zonelists(pg_data_t *pgdat)
> #endif
> }
>
> +#ifdef CONFIG_ZONE_DEVICE
> +void __ref memmap_init_zone_device(struct zone *zone, unsigned long pfn,
> + unsigned long size,
> + struct dev_pagemap *pgmap)
> +{
> + struct pglist_data *pgdat = zone->zone_pgdat;
> + unsigned long zone_idx = zone_idx(zone);
> + unsigned long end_pfn = pfn + size;
> + unsigned long start = jiffies;
> + int nid = pgdat->node_id;
> + unsigned long nr_pages;
> +
> + if (WARN_ON_ONCE(!pgmap || !is_dev_zone(zone)))
> + return;
> +
> + /*
> + * The call to memmap_init_zone should have already taken care
> + * of the pages reserved for the memmap, so we can just jump to
> + * the end of that region and start processing the device pages.
> + */
> + if (pgmap->altmap_valid) {
> + struct vmem_altmap *altmap = &pgmap->altmap;
> +
> + pfn = altmap->base_pfn + vmem_altmap_offset(altmap);
> + }
> +
> + /* Record the number of pages we are about to initialize */
> + nr_pages = end_pfn - pfn;
> +
> + for (; pfn < end_pfn; pfn++) {
> + struct page *page = pfn_to_page(pfn);
> +
> + __init_single_page(page, pfn, zone_idx, nid);
> +
> + /*
> + * Mark page reserved as it will need to wait for onlining
> + * phase for it to be fully associated with a zone.
> + *
> + * We can use the non-atomic __set_bit operation for setting
> + * the flag as we are still initializing the pages.
> + */
> + __SetPageReserved(page);
> +
> + /*
> + * ZONE_DEVICE pages union ->lru with a ->pgmap back
> + * pointer and hmm_data. It is a bug if a ZONE_DEVICE
> + * page is ever freed or placed on a driver-private list.
> + */
> + page->pgmap = pgmap;
> + page->hmm_data = 0;
> +
> + /*
> + * Mark the block movable so that blocks are reserved for
> + * movable at startup. This will force kernel allocations
> + * to reserve their blocks rather than leaking throughout
> + * the address space during boot when many long-lived
> + * kernel allocations are made.
> + *
> + * bitmap is created for zone's valid pfn range. but memmap
> + * can be created for invalid pages (for alignment)
> + * check here not to call set_pageblock_migratetype() against
> + * pfn out of zone.
> + *
> + * Please note that MEMMAP_HOTPLUG path doesn't clear memmap
> + * because this is done early in sparse_add_one_section
> + */
> + if (!(pfn & (pageblock_nr_pages - 1))) {
> + set_pageblock_migratetype(page, MIGRATE_MOVABLE);
> + cond_resched();
> + }
> + }
> +
> + pr_info("%s initialised, %lu pages in %ums\n", dev_name(pgmap->dev),
> + nr_pages, jiffies_to_msecs(jiffies - start));
> +}
> +
> +#endif
> /*
> * Initially all pages are reserved - free ones are freed
> * up by free_all_bootmem() once the early boot process is
> @@ -5477,10 +5554,18 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>
> /*
> * Honor reservation requested by the driver for this ZONE_DEVICE
> - * memory
> + * memory. We limit the total number of pages to initialize to just
> + * those that might contain the memory mapping. We will defer the
> + * ZONE_DEVICE page initialization until after we have released
> + * the hotplug lock.
> */
> - if (altmap && start_pfn == altmap->base_pfn)
> + if (altmap && start_pfn == altmap->base_pfn) {
> start_pfn += altmap->reserve;
> + end_pfn = altmap->base_pfn +
> + vmem_altmap_offset(altmap);
> + } else if (zone == ZONE_DEVICE) {
> + end_pfn = start_pfn;
> + }
>
> for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> /*
>
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