+ mm-page_alloc-reuse-tail-struct-pages-for-compound-devmaps.patch added to -mm tree

* + mm-page_alloc-reuse-tail-struct-pages-for-compound-devmaps.patch added to -mm tree
@ 2022-04-20 21:41 Andrew Morton
  0 siblings, 0 replies; 3+ messages in thread
From: Andrew Morton @ 2022-04-20 21:41 UTC (permalink / raw)
  To: mm-commits, willy, vishal.l.verma, songmuchun, mike.kravetz, jgg,
	jane.chu, hch, dan.j.williams, corbet, joao.m.martins, akpm


The patch titled
     Subject: mm/page_alloc: reuse tail struct pages for compound devmaps
has been added to the -mm tree.  Its filename is
     mm-page_alloc-reuse-tail-struct-pages-for-compound-devmaps.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-reuse-tail-struct-pages-for-compound-devmaps.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-reuse-tail-struct-pages-for-compound-devmaps.patch

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------------------------------------------------------
From: Joao Martins <joao.m.martins@oracle.com>
Subject: mm/page_alloc: reuse tail struct pages for compound devmaps

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>
---

 mm/page_alloc.c |   17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

--- a/mm/page_alloc.c~mm-page_alloc-reuse-tail-struct-pages-for-compound-devmaps
+++ a/mm/page_alloc.c
@@ -6588,6 +6588,21 @@ static void __ref __init_zone_device_pag
 	}
 }
 
+/*
+ * 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,
@@ -6652,7 +6667,7 @@ void __ref memmap_init_zone_device(struc
 			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__,
_

Patches currently in -mm which might be from joao.m.martins@oracle.com are

mm-sparse-vmemmap-add-a-pgmap-argument-to-section-activation.patch
mm-sparse-vmemmap-refactor-core-of-vmemmap_populate_basepages-to-helper.patch
mm-hugetlb_vmemmap-move-comment-block-to-documentation-vm.patch
mm-sparse-vmemmap-improve-memory-savings-for-compound-devmaps.patch
mm-page_alloc-reuse-tail-struct-pages-for-compound-devmaps.patch


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