Let's prepend both kmalloc() and kmem_cache_alloc() allocations with the size header. It simplifies the slab API and guarantees that both kmem_cache_alloc() and kmalloc() memory could be freed by kfree(). meminfo right after the system boot, x86-64 on xfs, without the patch: Slab: 35456 kB the same, with the patch: Slab: 36100 kB Link: https://lore.kernel.org/lkml/20210929212347.1139666-1-rkovhaev@xxxxxxxxx Signed-off-by: Rustam Kovhaev <rkovhaev@xxxxxxxxx> --- v3: - Add SLOB_HDR_SIZE define - Remove references to minalign - Improve documentation wording v2: - Allocate compound pages in slob_alloc_node() - Use slob_free_pages() in kfree() - Update documentation --- Documentation/core-api/memory-allocation.rst | 12 +- mm/slob.c | 132 +++++++++---------- 2 files changed, 68 insertions(+), 76 deletions(-) diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst index 5954ddf6ee13..31806d5ebeec 100644 --- a/Documentation/core-api/memory-allocation.rst +++ b/Documentation/core-api/memory-allocation.rst @@ -170,7 +170,11 @@ should be used if a part of the cache might be copied to the userspace. After the cache is created kmem_cache_alloc() and its convenience wrappers can allocate memory from that cache. -When the allocated memory is no longer needed it must be freed. You can -use kvfree() for the memory allocated with `kmalloc`, `vmalloc` and -`kvmalloc`. The slab caches should be freed with kmem_cache_free(). And -don't forget to destroy the cache with kmem_cache_destroy(). +When the allocated memory is no longer needed it must be freed. +Objects allocated by `kmalloc` can be freed with `kfree` or `kvfree`. +Objects allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free` +or also by `kfree` or `kvfree`. +Memory allocated by `vmalloc` can be freed with `vfree` or `kvfree`. +Memory allocated by `kvmalloc` can be freed with `kvfree`. +Caches created by `kmem_cache_create` should be freed with +`kmem_cache_destroy`. diff --git a/mm/slob.c b/mm/slob.c index 74d3f6e60666..4a4f3fe40a59 100644 --- a/mm/slob.c +++ b/mm/slob.c @@ -25,23 +25,18 @@ * into the free list in address order, so this is effectively an * address-ordered first fit. * - * Above this is an implementation of kmalloc/kfree. Blocks returned - * from kmalloc are prepended with a 4-byte header with the kmalloc size. - * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls - * alloc_pages() directly, allocating compound pages so the page order - * does not have to be separately tracked. - * These objects are detected in kfree() because PageSlab() - * is false for them. + * Blocks that are less than (PAGE_SIZE - SLOB_HDR_SIZE) are prepended with + * a 4-byte header with the size. Larger blocks do not have the header and + * SLOB calls alloc_pages() directly, allocating compound pages so the + * page order does not have to be separately tracked. These objects are + * detected in kfree() because PageSlab() is false for them. * * SLAB is emulated on top of SLOB by simply calling constructors and * destructors for every SLAB allocation. Objects are returned with the * 4-byte alignment unless the SLAB_HWCACHE_ALIGN flag is set, in which * case the low-level allocator will fragment blocks to create the proper - * alignment. Again, objects of page-size or greater are allocated by - * calling alloc_pages(). As SLAB objects know their size, no separate - * size bookkeeping is necessary and there is essentially no allocation - * space overhead, and compound pages aren't needed for multi-page - * allocations. + * alignment. Again, objects of (PAGE_SIZE - SLOB_HDR_SIZE) or greater are + * allocated by calling alloc_pages(). * * NUMA support in SLOB is fairly simplistic, pushing most of the real * logic down to the page allocator, and simply doing the node accounting @@ -88,6 +83,8 @@ typedef s16 slobidx_t; typedef s32 slobidx_t; #endif +#define SLOB_HDR_SIZE max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN) + struct slob_block { slobidx_t units; }; @@ -207,12 +204,14 @@ static void *slob_new_pages(gfp_t gfp, int order, int node) return page_address(page); } -static void slob_free_pages(void *b, int order) +static void slob_free_pages(struct page *sp, int order) { - struct page *sp = virt_to_page(b); - - if (current->reclaim_state) - current->reclaim_state->reclaimed_slab += 1 << order; + if (PageSlab(sp)) { + __ClearPageSlab(sp); + page_mapcount_reset(sp); + if (current->reclaim_state) + current->reclaim_state->reclaimed_slab += 1 << order; + } mod_node_page_state(page_pgdat(sp), NR_SLAB_UNRECLAIMABLE_B, -(PAGE_SIZE << order)); @@ -247,9 +246,7 @@ static void *slob_page_alloc(struct page *sp, size_t size, int align, /* * 'aligned' will hold the address of the slob block so that the * address 'aligned'+'align_offset' is aligned according to the - * 'align' parameter. This is for kmalloc() which prepends the - * allocated block with its size, so that the block itself is - * aligned when needed. + * 'align' parameter. */ if (align) { aligned = (slob_t *) @@ -373,25 +370,26 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node, } if (unlikely(gfp & __GFP_ZERO)) memset(b, 0, size); - return b; + /* Write size in the header */ + *(unsigned int *)b = size - align_offset; + return (void *)b + align_offset; } /* * slob_free: entry point into the slob allocator. */ -static void slob_free(void *block, int size) +static void slob_free(void *block) { struct page *sp; - slob_t *prev, *next, *b = (slob_t *)block; + slob_t *prev, *next, *b = block - SLOB_HDR_SIZE; + unsigned int size; slobidx_t units; unsigned long flags; struct list_head *slob_list; - if (unlikely(ZERO_OR_NULL_PTR(block))) - return; - BUG_ON(!size); - - sp = virt_to_page(block); + size = *(unsigned int *)b + SLOB_HDR_SIZE; + BUG_ON(!size || size >= PAGE_SIZE); + sp = virt_to_page(b); units = SLOB_UNITS(size); spin_lock_irqsave(&slob_lock, flags); @@ -401,9 +399,7 @@ static void slob_free(void *block, int size) if (slob_page_free(sp)) clear_slob_page_free(sp); spin_unlock_irqrestore(&slob_lock, flags); - __ClearPageSlab(sp); - page_mapcount_reset(sp); - slob_free_pages(b, 0); + slob_free_pages(sp, 0); return; } @@ -476,36 +472,29 @@ void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page) static __always_inline void * __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller) { - unsigned int *m; - int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN); void *ret; gfp &= gfp_allowed_mask; might_alloc(gfp); - if (size < PAGE_SIZE - minalign) { - int align = minalign; + if (size < PAGE_SIZE - SLOB_HDR_SIZE) { + int align = SLOB_HDR_SIZE; /* * For power of two sizes, guarantee natural alignment for * kmalloc()'d objects. */ if (is_power_of_2(size)) - align = max(minalign, (int) size); + align = max(align, (int) size); if (!size) return ZERO_SIZE_PTR; - m = slob_alloc(size + minalign, gfp, align, node, minalign); - - if (!m) - return NULL; - *m = size; - ret = (void *)m + minalign; + ret = slob_alloc(size + SLOB_HDR_SIZE, gfp, align, node, SLOB_HDR_SIZE); trace_kmalloc_node(caller, ret, - size, size + minalign, gfp, node); + size, size + SLOB_HDR_SIZE, gfp, node); } else { unsigned int order = get_order(size); @@ -553,26 +542,17 @@ void kfree(const void *block) kmemleak_free(block); sp = virt_to_page(block); - if (PageSlab(sp)) { - int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN); - unsigned int *m = (unsigned int *)(block - align); - slob_free(m, *m + align); - } else { - unsigned int order = compound_order(sp); - mod_node_page_state(page_pgdat(sp), NR_SLAB_UNRECLAIMABLE_B, - -(PAGE_SIZE << order)); - __free_pages(sp, order); - - } + if (PageSlab(sp)) + slob_free((void *)block); + else + slob_free_pages(sp, compound_order(sp)); } EXPORT_SYMBOL(kfree); -/* can't use ksize for kmem_cache_alloc memory, only kmalloc */ size_t __ksize(const void *block) { struct page *sp; - int align; - unsigned int *m; + unsigned int size; BUG_ON(!block); if (unlikely(block == ZERO_SIZE_PTR)) @@ -582,9 +562,8 @@ size_t __ksize(const void *block) if (unlikely(!PageSlab(sp))) return page_size(sp); - align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN); - m = (unsigned int *)(block - align); - return SLOB_UNITS(*m) * SLOB_UNIT; + size = *(unsigned int *)(block - SLOB_HDR_SIZE); + return SLOB_UNITS(size) * SLOB_UNIT; } EXPORT_SYMBOL(__ksize); @@ -606,16 +585,19 @@ static void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node) might_alloc(flags); - if (c->size < PAGE_SIZE) { - b = slob_alloc(c->size, flags, c->align, node, 0); + if (c->size < PAGE_SIZE - SLOB_HDR_SIZE) { + b = slob_alloc(c->size + SLOB_HDR_SIZE, flags, c->align, node, SLOB_HDR_SIZE); trace_kmem_cache_alloc_node(_RET_IP_, b, c->object_size, - SLOB_UNITS(c->size) * SLOB_UNIT, + SLOB_UNITS(c->size + SLOB_HDR_SIZE) * SLOB_UNIT, flags, node); } else { - b = slob_new_pages(flags, get_order(c->size), node); + unsigned int order = get_order(c->size); + + if (likely(order)) + flags |= __GFP_COMP; + b = slob_new_pages(flags, order, node); trace_kmem_cache_alloc_node(_RET_IP_, b, c->object_size, - PAGE_SIZE << get_order(c->size), - flags, node); + PAGE_SIZE << order, flags, node); } if (b && c->ctor) { @@ -647,12 +629,18 @@ void *kmem_cache_alloc_node(struct kmem_cache *cachep, gfp_t gfp, int node) EXPORT_SYMBOL(kmem_cache_alloc_node); #endif -static void __kmem_cache_free(void *b, int size) +static void __kmem_cache_free(void *b) { - if (size < PAGE_SIZE) - slob_free(b, size); + struct page *sp; + + if (unlikely(ZERO_OR_NULL_PTR(b))) + return; + + sp = virt_to_page(b); + if (PageSlab(sp)) + slob_free(b); else - slob_free_pages(b, get_order(size)); + slob_free_pages(sp, compound_order(sp)); } static void kmem_rcu_free(struct rcu_head *head) @@ -660,7 +648,7 @@ static void kmem_rcu_free(struct rcu_head *head) struct slob_rcu *slob_rcu = (struct slob_rcu *)head; void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu)); - __kmem_cache_free(b, slob_rcu->size); + __kmem_cache_free(b); } void kmem_cache_free(struct kmem_cache *c, void *b) @@ -672,7 +660,7 @@ void kmem_cache_free(struct kmem_cache *c, void *b) slob_rcu->size = c->size; call_rcu(&slob_rcu->head, kmem_rcu_free); } else { - __kmem_cache_free(b, c->size); + __kmem_cache_free(b); } trace_kmem_cache_free(_RET_IP_, b, c->name); -- 2.30.2
