zsmalloc: introduce zs_huge_class_size()
Patch series "zsmalloc/zram: drop zram's max_zpage_size", v3. ZRAM's max_zpage_size is a bad thing. It forces zsmalloc to store normal objects as huge ones, which results in bigger zsmalloc memory usage. Drop it and use actual zsmalloc huge-class value when decide if the object is huge or not. This patch (of 2): Not every object can be share its zspage with other objects, e.g. when the object is as big as zspage or nearly as big a zspage. For such objects zsmalloc has a so called huge class - every object which belongs to huge class consumes the entire zspage (which consists of a physical page). On x86_64, PAGE_SHIFT 12 box, the first non-huge class size is 3264, so starting down from size 3264, objects can share page(-s) and thus minimize memory wastage. ZRAM, however, has its own statically defined watermark for huge objects, namely "3 * PAGE_SIZE / 4 = 3072", and forcibly stores every object larger than this watermark (3072) as a PAGE_SIZE object, in other words, to a huge class, while zsmalloc can keep some of those objects in non-huge classes. This results in increased memory consumption. zsmalloc knows better if the object is huge or not. Introduce zs_huge_class_size() function which tells if the given object can be stored in one of non-huge classes or not. This will let us to drop ZRAM's huge object watermark and fully rely on zsmalloc when we decide if the object is huge. [sergey.senozhatsky.work@gmail.com: add pool param to zs_huge_class_size()] Link: http://lkml.kernel.org/r/20180314081833.1096-2-sergey.senozhatsky@gmail.com Link: http://lkml.kernel.org/r/20180306070639.7389-2-sergey.senozhatsky@gmail.com Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -47,6 +47,8 @@ void zs_destroy_pool(struct zs_pool *pool);
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unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t flags);
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void zs_free(struct zs_pool *pool, unsigned long obj);
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size_t zs_huge_class_size(struct zs_pool *pool);
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void *zs_map_object(struct zs_pool *pool, unsigned long handle,
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enum zs_mapmode mm);
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void zs_unmap_object(struct zs_pool *pool, unsigned long handle);
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@ -193,6 +193,7 @@ static struct vfsmount *zsmalloc_mnt;
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* (see: fix_fullness_group())
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*/
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static const int fullness_threshold_frac = 4;
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static size_t huge_class_size;
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struct size_class {
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spinlock_t lock;
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@ -1407,6 +1408,25 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
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}
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EXPORT_SYMBOL_GPL(zs_unmap_object);
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/**
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* zs_huge_class_size() - Returns the size (in bytes) of the first huge
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* zsmalloc &size_class.
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* @pool: zsmalloc pool to use
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*
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* The function returns the size of the first huge class - any object of equal
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* or bigger size will be stored in zspage consisting of a single physical
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* page.
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*
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* Context: Any context.
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*
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* Return: the size (in bytes) of the first huge zsmalloc &size_class.
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*/
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size_t zs_huge_class_size(struct zs_pool *pool)
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{
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return huge_class_size;
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}
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EXPORT_SYMBOL_GPL(zs_huge_class_size);
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static unsigned long obj_malloc(struct size_class *class,
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struct zspage *zspage, unsigned long handle)
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{
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@ -2363,6 +2383,27 @@ struct zs_pool *zs_create_pool(const char *name)
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pages_per_zspage = get_pages_per_zspage(size);
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objs_per_zspage = pages_per_zspage * PAGE_SIZE / size;
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/*
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* We iterate from biggest down to smallest classes,
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* so huge_class_size holds the size of the first huge
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* class. Any object bigger than or equal to that will
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* endup in the huge class.
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*/
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if (pages_per_zspage != 1 && objs_per_zspage != 1 &&
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!huge_class_size) {
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huge_class_size = size;
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/*
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* The object uses ZS_HANDLE_SIZE bytes to store the
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* handle. We need to subtract it, because zs_malloc()
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* unconditionally adds handle size before it performs
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* size class search - so object may be smaller than
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* huge class size, yet it still can end up in the huge
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* class because it grows by ZS_HANDLE_SIZE extra bytes
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* right before class lookup.
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*/
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huge_class_size -= (ZS_HANDLE_SIZE - 1);
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}
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/*
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* size_class is used for normal zsmalloc operation such
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* as alloc/free for that size. Although it is natural that we
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