+ mm-add-folio_estimated_sharers.patch added to mm-unstable branch

+ mm-add-folio_estimated_sharers.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: add folio_estimated_sharers()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-add-folio_estimated_sharers.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-add-folio_estimated_sharers.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: "Vishal Moola (Oracle)" <vishal.moola@gmail.com>
Subject: mm: add folio_estimated_sharers()
Date: Mon, 30 Jan 2023 12:18:28 -0800

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>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: "Yin, Fengwei" <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/include/linux/mm.h~mm-add-folio_estimated_sharers
+++ a/include/linux/mm.h
@@ -1911,6 +1911,24 @@ static inline size_t folio_size(struct f
 	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)
 {
_

Patches currently in -mm which might be from vishal.moola@gmail.com are

mm-khugepaged-introduce-release_pte_folio-to-replace-release_pte_page.patch
mm-khugepaged-convert-release_pte_pages-to-use-folios.patch
pagemap-add-filemap_grab_folio.patch
filemap-added-filemap_get_folios_tag.patch
filemap-convert-__filemap_fdatawait_range-to-use-filemap_get_folios_tag.patch
page-writeback-convert-write_cache_pages-to-use-filemap_get_folios_tag.patch
afs-convert-afs_writepages_region-to-use-filemap_get_folios_tag.patch
btrfs-convert-btree_write_cache_pages-to-use-filemap_get_folio_tag.patch
btrfs-convert-extent_write_cache_pages-to-use-filemap_get_folios_tag.patch
ceph-convert-ceph_writepages_start-to-use-filemap_get_folios_tag.patch
cifs-convert-wdata_alloc_and_fillpages-to-use-filemap_get_folios_tag.patch
ext4-convert-mpage_prepare_extent_to_map-to-use-filemap_get_folios_tag.patch
f2fs-convert-f2fs_fsync_node_pages-to-use-filemap_get_folios_tag.patch
f2fs-convert-f2fs_flush_inline_data-to-use-filemap_get_folios_tag.patch
f2fs-convert-f2fs_sync_node_pages-to-use-filemap_get_folios_tag.patch
f2fs-convert-f2fs_write_cache_pages-to-use-filemap_get_folios_tag.patch
f2fs-convert-last_fsync_dnode-to-use-filemap_get_folios_tag.patch
f2fs-convert-f2fs_sync_meta_pages-to-use-filemap_get_folios_tag.patch
gfs2-convert-gfs2_write_cache_jdata-to-use-filemap_get_folios_tag.patch
nilfs2-convert-nilfs_lookup_dirty_data_buffers-to-use-filemap_get_folios_tag.patch
nilfs2-convert-nilfs_lookup_dirty_node_buffers-to-use-filemap_get_folios_tag.patch
nilfs2-convert-nilfs_btree_lookup_dirty_buffers-to-use-filemap_get_folios_tag.patch
nilfs2-convert-nilfs_copy_dirty_pages-to-use-filemap_get_folios_tag.patch
nilfs2-convert-nilfs_clear_dirty_pages-to-use-filemap_get_folios_tag.patch
filemap-remove-find_get_pages_range_tag.patch
mm-add-folio_estimated_sharers.patch
mm-mempolicy-convert-queue_pages_pmd-to-queue_folios_pmd.patch
mm-mempolicy-convert-queue_pages_pte_range-to-queue_folios_pte_range.patch
mm-mempolicy-convert-queue_pages_hugetlb-to-queue_folios_hugetlb.patch
mm-mempolicy-convert-queue_pages_required-to-queue_folio_required.patch
mm-mempolicy-convert-migrate_page_add-to-migrate_folio_add.patch