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mm/page_alloc: reuse tail struct pages for compound devmaps

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Currently memmap_init_zone_device() ends up initializing 32768 pages when
it only needs to initialize 128 given tail page reuse.  That number is
worse with 1GB compound pages, 262144 instead of 128.  Update
memmap_init_zone_device() to skip redundant initialization, detailed
below.

When a pgmap @vmemmap_shift is set, all pages are mapped at a given huge
page alignment and use compound pages to describe them as opposed to a
struct per 4K.

With @vmemmap_shift > 0 and when struct pages are stored in ram (!altmap)
most tail pages are reused.  Consequently, the amount of unique struct
pages is a lot smaller than the total amount of struct pages being mapped.

The altmap path is left alone since it does not support memory savings
based on compound pages devmap.

Link: https://lkml.kernel.org/r/20220420155310.9712-6-joao.m.martins@oracle.com
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Joao Martins 2022-04-28 23:16:16 -07:00 committed by akpm
parent 4917f55b4e
commit 6fd3620b34
1 changed files with 16 additions and 1 deletions
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17
mm/page_alloc.c
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@ -6596,6 +6596,21 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
}
}
/*
* With compound page geometry and when struct pages are stored in ram most
* tail pages are reused. Consequently, the amount of unique struct pages to
* initialize is a lot smaller that the total amount of struct pages being
* mapped. This is a paired / mild layering violation with explicit knowledge
* of how the sparse_vmemmap internals handle compound pages in the lack
* of an altmap. See vmemmap_populate_compound_pages().
*/
static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,
unsigned long nr_pages)
{
return is_power_of_2(sizeof(struct page)) &&
!altmap ? 2 * (PAGE_SIZE / sizeof(struct page)) : nr_pages;
}
static void __ref memmap_init_compound(struct page *head,
unsigned long head_pfn,
unsigned long zone_idx, int nid,
@ -6660,7 +6675,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
continue;
memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
pfns_per_compound);
compound_nr_pages(altmap, pfns_per_compound));
}
pr_info("%s initialised %lu pages in %ums\n", __func__,