linux-kernel - Re: [patch 1/2] mm, page_alloc: extend kernelcore and movablecore for percent

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Date:   Thu, 15 Feb 2018 12:14:05 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-doc@...r.kernel.org
Subject: Re: [patch 1/2] mm, page_alloc: extend kernelcore and movablecore
 for percent

On Thu, Feb 15, 2018 at 09:49:00AM -0600, Christopher Lameter wrote:
> On Thu, 15 Feb 2018, Matthew Wilcox wrote:
> 
> > What if ... on startup, slab allocated a MAX_ORDER page for itself.
> > It would then satisfy its own page allocation requests from this giant
> > page.  If we start to run low on memory in the rest of the system, slab
> > can be induced to return some of it via its shrinker.  If slab runs low
> > on memory, it tries to allocate another MAX_ORDER page for itself.
> 
> The inducing of releasing memory back is not there but you can run SLUB
> with MAX_ORDER allocations by passing "slab_min_order=9" or so on bootup.

Maybe we should try this patch in order to automatically scale the slub
page size with the amount of memory in the machine?

diff --git a/mm/internal.h b/mm/internal.h
index e6bd35182dae..7059a8389194 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -167,6 +167,7 @@ extern void prep_compound_page(struct page *page, unsigned int order);
 extern void post_alloc_hook(struct page *page, unsigned int order,
 					gfp_t gfp_flags);
 extern int user_min_free_kbytes;
+extern unsigned long __meminitdata nr_kernel_pages;
 
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ef9c259db041..3c51bb22403f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -264,7 +264,7 @@ int min_free_kbytes = 1024;
 int user_min_free_kbytes = -1;
 int watermark_scale_factor = 10;
 
-static unsigned long __meminitdata nr_kernel_pages;
+unsigned long __meminitdata nr_kernel_pages;
 static unsigned long __meminitdata nr_all_pages;
 static unsigned long __meminitdata dma_reserve;
 
diff --git a/mm/slub.c b/mm/slub.c
index e381728a3751..abca4a6e9b6c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4194,6 +4194,23 @@ void __init kmem_cache_init(void)
 
 	if (debug_guardpage_minorder())
 		slub_max_order = 0;
+	if (slub_min_order == 0) {
+		unsigned long numentries = nr_kernel_pages;
+
+		/*
+		 * Above 4GB, we start to care more about fragmenting large
+		 * pages than about using the minimum amount of memory.
+		 * Scale the slub page size at half the rate that we scale
+		 * the memory size; at 4GB we double the page size to 8k,
+		 * 16GB to 16k, 64GB to 32k, 256GB to 64k.
+		 */
+		while (numentries > (4UL << 30)) {
+			if (slub_min_order >= slub_max_order)
+				break;
+			slub_min_order++;
+			numentries /= 4;
+		}
+	}
 
 	kmem_cache_node = &boot_kmem_cache_node;
 	kmem_cache = &boot_kmem_cache;