On Mon, Jul 13, 2020 at 02:05:05PM +0300, Kirill A. Shutemov wrote:

On Mon, Jul 06, 2020 at 08:20:50PM +0300, Mike Rapoport wrote:

quoted

From: Mike Rapoport <redacted>

Removing a PAGE_SIZE page from the direct map every time such page is
allocated for a secret memory mapping will cause severe fragmentation of
the direct map. This fragmentation can be reduced by using PMD-size pages
as a pool for small pages for secret memory mappings.

Add a gen_pool per secretmem inode and lazily populate this pool with
PMD-size pages.

Signed-off-by: Mike Rapoport <redacted>
---
 mm/secretmem.c | 107 ++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 88 insertions(+), 19 deletions(-)

diff --git a/mm/secretmem.c b/mm/secretmem.c
index df8f8c958cc2..c6fcf6d76951 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c

@@ -5,6 +5,7 @@
 #include <linux/memfd.h>
 #include <linux/printk.h>
 #include <linux/pagemap.h>
+#include <linux/genalloc.h>
 #include <linux/pseudo_fs.h>
 #include <linux/set_memory.h>
 #include <linux/sched/signal.h>

@@ -23,24 +24,66 @@
 #define SECRETMEM_UNCACHED	0x2
 
 struct secretmem_ctx {
+	struct gen_pool *pool;
 	unsigned int mode;
 };
 
-static struct page *secretmem_alloc_page(gfp_t gfp)
+static int secretmem_pool_increase(struct secretmem_ctx *ctx, gfp_t gfp)
 {
-	/*
-	 * FIXME: use a cache of large pages to reduce the direct map
-	 * fragmentation
-	 */
-	return alloc_page(gfp);
+	unsigned long nr_pages = (1 << HPAGE_PMD_ORDER);
+	struct gen_pool *pool = ctx->pool;
+	unsigned long addr;
+	struct page *page;
+	int err;
+
+	page = alloc_pages(gfp, HPAGE_PMD_ORDER);
+	if (!page)
+		return -ENOMEM;
+
+	addr = (unsigned long)page_address(page);
+	split_page(page, HPAGE_PMD_ORDER);
+
+	err = gen_pool_add(pool, addr, HPAGE_PMD_SIZE, NUMA_NO_NODE);
+	if (err) {
+		__free_pages(page, HPAGE_PMD_ORDER);
+		return err;
+	}
+
+	__kernel_map_pages(page, nr_pages, 0);

It's worth nothing that unlike flush_tlb_kernel_range(),
__kernel_map_pages() only flushed local TLB, so other CPU may still have
access to the page. It's shouldn't be a blocker, but deserve a comment.

Sure.
 

quoted

+
+	return 0;
+}
+

-- 
Sincerely yours,
Mike.