+ mm-allow-deferred-splitting-of-arbitrary-large-anon-folios.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: allow deferred splitting of arbitrary large anon folios
has been added to the -mm mm-unstable branch.  Its filename is
     mm-allow-deferred-splitting-of-arbitrary-large-anon-folios.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-allow-deferred-splitting-of-arbitrary-large-anon-folios.patch

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

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------------------------------------------------------
From: Ryan Roberts <ryan.roberts@arm.com>
Subject: mm: allow deferred splitting of arbitrary large anon folios
Date: Thu, 20 Jul 2023 12:29:53 +0100

Patch series "Optimize large folio interaction with deferred split" v3.

A small series in support of my work to enable the use of large folios for
anonymous memory (known as "FLEXIBLE_THP" or "LARGE_ANON_FOLIO") [1].  It
first makes it possible to add large, non-pmd-mappable folios to the
deferred split queue.  Then it modifies zap_pte_range() to batch-remove
spans of physically contiguous pages from the rmap, which means that in
the common case, we elide the need to ever put the folio on the deferred
split queue, thus reducing lock contention and improving performance.

This becomes more visible once we have lots of large anonymous folios in
the system, and Huang Ying has suggested solving this needs to be a
prerequisit for merging the main FLEXIBLE_THP/LARGE_ANON_FOLIO work.

This patch (of 3):


In preparation for the introduction of large folios for anonymous memory,
we would like to be able to split them when they have unmapped subpages,
in order to free those unused pages under memory pressure.  So remove the
artificial requirement that the large folio needed to be at least
PMD-sized.

Link: https://lkml.kernel.org/r/20230720112955.643283-1-ryan.roberts@arm.com
Link: https://lkml.kernel.org/r/20230720112955.643283-2-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/rmap.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/rmap.c~mm-allow-deferred-splitting-of-arbitrary-large-anon-folios
+++ a/mm/rmap.c
@@ -1414,11 +1414,11 @@ void page_remove_rmap(struct page *page,
 		__lruvec_stat_mod_folio(folio, idx, -nr);
 
 		/*
-		 * Queue anon THP for deferred split if at least one
+		 * Queue anon large folio for deferred split if at least one
 		 * page of the folio is unmapped and at least one page
 		 * is still mapped.
 		 */
-		if (folio_test_pmd_mappable(folio) && folio_test_anon(folio))
+		if (folio_test_large(folio) && folio_test_anon(folio))
 			if (!compound || nr < nr_pmdmapped)
 				deferred_split_folio(folio);
 	}
_

Patches currently in -mm which might be from ryan.roberts@arm.com are

mm-allow-deferred-splitting-of-arbitrary-large-anon-folios.patch
mm-implement-folio_remove_rmap_range.patch
mm-batch-zap-large-anonymous-folio-pte-mappings.patch