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mm: add folio_estimated_sharers()

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Patch series "Convert various mempolicy.c functions to use folios", v4.

This patch series converts migrate_page_add() and queue_pages_required()
to migrate_folio_add() and queue_page_required().  It also converts the
callers of the functions to use folios as well, and introduces a helper
function to estimate the number of sharers of a folio.


This patch (of 6):

folio_estimated_sharers() takes in a folio and returns the precise number
of times the first subpage of the folio is mapped.

This function aims to provide an estimate for the number of sharers of a
folio.  This is necessary for folio conversions where we care about the
number of processes that share a folio, but don't necessarily want to
check every single page within that folio.

This is in contrast to folio_mapcount() which calculates the total number
of the times a folio and all its subpages are mapped.

Link: https://lkml.kernel.org/r/20230130201833.27042-1-vishal.moola@gmail.com
Link: https://lkml.kernel.org/r/20230130201833.27042-2-vishal.moola@gmail.com
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Jane Chu <jane.chu@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Vishal Moola (Oracle) 2023-01-30 12:18:28 -08:00 committed by Andrew Morton
parent 192a502203
commit fa4e3f5ffa
1 changed files with 18 additions and 0 deletions
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18
include/linux/mm.h
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@ -1916,6 +1916,24 @@ static inline size_t folio_size(struct folio *folio)
return PAGE_SIZE << folio_order(folio);
}
/**
* folio_estimated_sharers - Estimate the number of sharers of a folio.
* @folio: The folio.
*
* folio_estimated_sharers() aims to serve as a function to efficiently
* estimate the number of processes sharing a folio. This is done by
* looking at the precise mapcount of the first subpage in the folio, and
* assuming the other subpages are the same. This may not be true for large
* folios. If you want exact mapcounts for exact calculations, look at
* page_mapcount() or folio_total_mapcount().
*
* Return: The estimated number of processes sharing a folio.
*/
static inline int folio_estimated_sharers(struct folio *folio)
{
return page_mapcount(folio_page(folio, 0));
}
#ifndef HAVE_ARCH_MAKE_PAGE_ACCESSIBLE
static inline int arch_make_page_accessible(struct page *page)
{