Re: [PATCH] mm/zsmalloc: include sparsemem.h for MAX_PHYSMEM_BITS

[Minchan Kim <minchan@kernel.org>]

On Tue, Nov 10, 2020 at 06:21:55PM +0200, Mike Rapoport wrote:
> On Tue, Nov 10, 2020 at 12:21:11PM +0100, Arnd Bergmann wrote:
> > On Tue, Nov 10, 2020 at 10:58 AM Mike Rapoport <rppt@kernel.org> wrote:
> > > > >
> > > > > asm/sparsemem.h is not available on some architectures.
> > > > > It's better to use linux/mmzone.h instead.
> > 
> > Ah, I missed that, too.
> > 
> > > > Hm, linux/mmzone.h only includes asm/sparsemem.h when CONFIG_SPARSEMEM
> > > > is enabled. However, on ARM at least I can have configurations without
> > > > CONFIG_SPARSEMEM and physical address extension on (e.g.
> > > > multi_v7_defconfig + CONFIG_LPAE + CONFIG_ZSMALLOC).
> > > >
> > > > While sparsemem seems to be a good idea with LPAE it really seems not
> > > > required (see also https://lore.kernel.org/patchwork/patch/567589/).
> > > >
> > > > There seem to be also other architectures which define MAX_PHYSMEM_BITS
> > > > only when SPARSEMEM is enabled, e.g.
> > > > arch/riscv/include/asm/sparsemem.h...
> > > >
> > > > Not sure how to get out of this.. Maybe make ZSMALLOC dependent on
> > > > SPARSEMEM? It feels a bit silly restricting ZSMALLOC selection only due
> > > > to a compile time define...
> > >
> > > I think we can define MAX_POSSIBLE_PHYSMEM_BITS in one of
> > > arch/arm/inclide/asm/pgtable-{2,3}level-*.h headers to values supported
> > > by !LPAE and LPAE.
> > 
> > Good idea. I wonder what other architectures need the same though.
> > Here are some I found:
> > 
> > $ git grep -l PHYS_ADDR_T_64BIT arch | grep Kconfig
> > arch/arc/Kconfig
> > arch/arm/mm/Kconfig
> > arch/mips/Kconfig
> > arch/powerpc/platforms/Kconfig.cputype
> > arch/x86/Kconfig
> > 
> > arch/arc has a CONFIG_ARC_HAS_PAE40 option
> > arch/riscv has 34-bit addressing in rv32 mode
> > arch/mips has up to 40 bits with mips32r3 XPA, but I don't know what
> >     supports that
> > 
> > arch/powerpc has this:
> > config PHYS_64BIT
> >         bool 'Large physical address support' if E500 || PPC_86xx
> >         depends on (44x || E500 || PPC_86xx) && !PPC_83xx && !PPC_82xx
> > 
> > Apparently all three (4xx, e500v2, mpc86xx/e600) do 36-bit physical
> > addressing, but each one has a different page table format.
> > 
> > Microblaze has physical address extensions, but neither those nor
> > 64-bit mode have so far made it into the kernel.
> > 
> > To be on the safe side, we could provoke a compile-time error
> > when CONFIG_PHYS_ADDR_T_64BIT is set on a 32-bit
> > architecture, but MAX_POSSIBLE_PHYSMEM_BITS is not set.
> 
> Maybe compile time warning and a runtime error in zs_init() if 32 bit
> machine has memory above 4G?

I guess max_pfn will represent maximum pfn configued in the system
and will not be changed in the runtime. If it's true, how about this?
(didn't test at all but just for RFC)

From 2f51a743a08d10c787a36912515a91826693e308 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Tue, 10 Nov 2020 15:17:12 -0800
Subject: [PATCH] zsmalloc: do not support if system has too big memory

zsmalloc encode object location into unsigned long so if the system
has too big memory to encode the object location into BITS_PER_LONG,
it should return the error. Otherwise, system will be crash.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/zsmalloc.c | 82 ++++++++++++++++++++++++++++-----------------------
 1 file changed, 45 insertions(+), 37 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 662ee420706f..13552f412ca1 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -87,19 +87,8 @@
  * This is made more complicated by various memory models and PAE.
  */
 
-#ifndef MAX_POSSIBLE_PHYSMEM_BITS
-#ifdef MAX_PHYSMEM_BITS
-#define MAX_POSSIBLE_PHYSMEM_BITS MAX_PHYSMEM_BITS
-#else
-/*
- * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just
- * be PAGE_SHIFT
- */
-#define MAX_POSSIBLE_PHYSMEM_BITS BITS_PER_LONG
-#endif
-#endif
-
-#define _PFN_BITS		(MAX_POSSIBLE_PHYSMEM_BITS - PAGE_SHIFT)
+static unsigned int pfn_bits;
+static unsigned int obj_index_bits;
 
 /*
  * Memory for allocating for handle keeps object position by
@@ -119,18 +108,20 @@
  */
 #define OBJ_ALLOCATED_TAG 1
 #define OBJ_TAG_BITS 1
-#define OBJ_INDEX_BITS	(BITS_PER_LONG - _PFN_BITS - OBJ_TAG_BITS)
-#define OBJ_INDEX_MASK	((_AC(1, UL) << OBJ_INDEX_BITS) - 1)
+static unsigned int obj_index_mask;
 
 #define FULLNESS_BITS	2
 #define CLASS_BITS	8
 #define ISOLATED_BITS	3
 #define MAGIC_VAL_BITS	8
 
-#define MAX(a, b) ((a) >= (b) ? (a) : (b))
-/* ZS_MIN_ALLOC_SIZE must be multiple of ZS_ALIGN */
-#define ZS_MIN_ALLOC_SIZE \
-	MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
+/* zs_min_alloc_size must be multiple of ZS_ALIGN */
+int zs_min_alloc_size(void)
+{
+	return max_t(unsigned long, 32, ZS_MAX_PAGES_PER_ZSPAGE <<
+			PAGE_SHIFT >> obj_index_bits);
+}
+
 /* each chunk includes extra space to keep handle */
 #define ZS_MAX_ALLOC_SIZE	PAGE_SIZE
 
@@ -144,12 +135,11 @@
  *    determined). NOTE: all those class sizes must be set as multiple of
  *    ZS_ALIGN to make sure link_free itself never has to span 2 pages.
  *
- *  ZS_MIN_ALLOC_SIZE and ZS_SIZE_CLASS_DELTA must be multiple of ZS_ALIGN
+ *  zs_min_alloc_size and ZS_SIZE_CLASS_DELTA must be multiple of ZS_ALIGN
  *  (reason above)
  */
 #define ZS_SIZE_CLASS_DELTA	(PAGE_SIZE >> CLASS_BITS)
-#define ZS_SIZE_CLASSES	(DIV_ROUND_UP(ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE, \
-				      ZS_SIZE_CLASS_DELTA) + 1)
+static unsigned int zs_size_classes;
 
 enum fullness_group {
 	ZS_EMPTY,
@@ -253,7 +243,7 @@ struct link_free {
 struct zs_pool {
 	const char *name;
 
-	struct size_class *size_class[ZS_SIZE_CLASSES];
+	struct size_class **size_class;
 	struct kmem_cache *handle_cachep;
 	struct kmem_cache *zspage_cachep;
 
@@ -541,11 +531,11 @@ static int get_size_class_index(int size)
 {
 	int idx = 0;
 
-	if (likely(size > ZS_MIN_ALLOC_SIZE))
-		idx = DIV_ROUND_UP(size - ZS_MIN_ALLOC_SIZE,
+	if (likely(size > zs_min_alloc_size()))
+		idx = DIV_ROUND_UP(size - zs_min_alloc_size(),
 				ZS_SIZE_CLASS_DELTA);
 
-	return min_t(int, ZS_SIZE_CLASSES - 1, idx);
+	return min_t(int, zs_size_classes - 1, idx);
 }
 
 /* type can be of enum type zs_stat_type or fullness_group */
@@ -605,7 +595,7 @@ static int zs_stats_size_show(struct seq_file *s, void *v)
 			"obj_allocated", "obj_used", "pages_used",
 			"pages_per_zspage", "freeable");
 
-	for (i = 0; i < ZS_SIZE_CLASSES; i++) {
+	for (i = 0; i < zs_size_classes; i++) {
 		class = pool->size_class[i];
 
 		if (class->index != i)
@@ -845,8 +835,8 @@ static void obj_to_location(unsigned long obj, struct page **page,
 				unsigned int *obj_idx)
 {
 	obj >>= OBJ_TAG_BITS;
-	*page = pfn_to_page(obj >> OBJ_INDEX_BITS);
-	*obj_idx = (obj & OBJ_INDEX_MASK);
+	*page = pfn_to_page(obj >> obj_index_bits);
+	*obj_idx = (obj & obj_index_mask);
 }
 
 /**
@@ -858,8 +848,8 @@ static unsigned long location_to_obj(struct page *page, unsigned int obj_idx)
 {
 	unsigned long obj;
 
-	obj = page_to_pfn(page) << OBJ_INDEX_BITS;
-	obj |= obj_idx & OBJ_INDEX_MASK;
+	obj = page_to_pfn(page) << obj_index_bits;
+	obj |= obj_idx & obj_index_mask;
 	obj <<= OBJ_TAG_BITS;
 
 	return obj;
@@ -2202,7 +2192,7 @@ static void async_free_zspage(struct work_struct *work)
 	struct zs_pool *pool = container_of(work, struct zs_pool,
 					free_work);
 
-	for (i = 0; i < ZS_SIZE_CLASSES; i++) {
+	for (i = 0; i < zs_size_classes; i++) {
 		class = pool->size_class[i];
 		if (class->index != i)
 			continue;
@@ -2320,7 +2310,7 @@ unsigned long zs_compact(struct zs_pool *pool)
 	int i;
 	struct size_class *class;
 
-	for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
+	for (i = zs_size_classes - 1; i >= 0; i--) {
 		class = pool->size_class[i];
 		if (!class)
 			continue;
@@ -2366,7 +2356,7 @@ static unsigned long zs_shrinker_count(struct shrinker *shrinker,
 	struct zs_pool *pool = container_of(shrinker, struct zs_pool,
 			shrinker);
 
-	for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
+	for (i = zs_size_classes - 1; i >= 0; i--) {
 		class = pool->size_class[i];
 		if (!class)
 			continue;
@@ -2427,18 +2417,20 @@ struct zs_pool *zs_create_pool(const char *name)
 	if (create_cache(pool))
 		goto err;
 
+	pool->size_class = kmalloc(sizeof(void *) * zs_size_classes, GFP_KERNEL);
+
 	/*
 	 * Iterate reversely, because, size of size_class that we want to use
 	 * for merging should be larger or equal to current size.
 	 */
-	for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
+	for (i = zs_size_classes - 1; i >= 0; i--) {
 		int size;
 		int pages_per_zspage;
 		int objs_per_zspage;
 		struct size_class *class;
 		int fullness = 0;
 
-		size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
+		size = zs_min_alloc_size() + i * ZS_SIZE_CLASS_DELTA;
 		if (size > ZS_MAX_ALLOC_SIZE)
 			size = ZS_MAX_ALLOC_SIZE;
 		pages_per_zspage = get_pages_per_zspage(size);
@@ -2528,7 +2520,7 @@ void zs_destroy_pool(struct zs_pool *pool)
 	zs_unregister_migration(pool);
 	zs_pool_stat_destroy(pool);
 
-	for (i = 0; i < ZS_SIZE_CLASSES; i++) {
+	for (i = 0; i < zs_size_classes; i++) {
 		int fg;
 		struct size_class *class = pool->size_class[i];
 
@@ -2547,6 +2539,7 @@ void zs_destroy_pool(struct zs_pool *pool)
 		kfree(class);
 	}
 
+	kfree(pool->size_class);
 	destroy_cache(pool);
 	kfree(pool->name);
 	kfree(pool);
@@ -2557,6 +2550,21 @@ static int __init zs_init(void)
 {
 	int ret;
 
+	/*
+	 * If BITS_PER_LONG is not big enough to encode metadata(e.g., object
+	 * location and some tags), it could't work at this moment.
+	 */
+	pfn_bits = ilog2(max_pfn) + 1;
+	if (BITS_PER_LONG - OBJ_TAG_BITS - pfn_bits < 0) {
+		pr_warn("max_pfn %lu is too large for zsmalloc\n",
+				max_pfn);
+		return -EFBIG;
+	}
+
+	obj_index_bits = BITS_PER_LONG - OBJ_TAG_BITS - pfn_bits;
+	obj_index_mask = (1 << obj_index_bits) - 1;
+	zs_size_classes = (DIV_ROUND_UP(ZS_MAX_ALLOC_SIZE - zs_min_alloc_size(),  ZS_SIZE_CLASS_DELTA) + 1);
+
 	ret = zsmalloc_mount();
 	if (ret)
 		goto out;
-- 
2.29.2.299.gdc1121823c-goog