• Joao Martins's avatar
    mm/page_alloc: reuse tail struct pages for compound devmaps · 6fd3620b
    Joao Martins authored
    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.comSigned-off-by: default avatarJoao Martins <joao.m.martins@oracle.com>
    Reviewed-by: default avatarMuchun 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: default avatarAndrew Morton <akpm@linux-foundation.org>
    6fd3620b
page_alloc.c 267 KB