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SubjectRe: [PATCH v4 3/5] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap
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On 9/21/2018 12:50 PM, Pasha Tatashin wrote:
>
>
> On 9/20/18 6:29 PM, Alexander Duyck wrote:
>> 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@linux.intel.com>
>
>> +void __ref memmap_init_zone_device(struct zone *zone,
>> + unsigned long start_pfn,
>> + unsigned long size,
>> + struct dev_pagemap *pgmap)
>> +{
>> + unsigned long pfn, end_pfn = start_pfn + size;
>> + struct pglist_data *pgdat = zone->zone_pgdat;
>> + unsigned long zone_idx = zone_idx(zone);
>> + unsigned long start = jiffies;
>> + int nid = pgdat->node_id;
>> +
>> + 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;
>> +
>> + start_pfn = altmap->base_pfn + vmem_altmap_offset(altmap);
>> + size = end_pfn - start_pfn;
>> + }
>> +
>> + for (pfn = start_pfn; 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;
>
> __init_single_page()
> mm_zero_struct_page()
>
> Takes care of zeroing, no need to do another store here.

The problem is __init_singe_page also calls INIT_LIST_HEAD which I
believe sets the prev pointer which overlaps with hmm_data.

>
> Looks good otherwise.
>
> Reviewed-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
>

Thanks for the review.

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