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e3483a5f3a
Tmem, as originally specified, assumes that "get" operations performed on persistent pools never flush the page of data out of tmem on a successful get, waiting instead for a flush operation. This is intended to mimic the model of a swap disk, where a disk read is non-destructive. Unlike a disk, however, freeing up the RAM can be valuable. Over the years that frontswap was in the review process, several reviewers (and notably Hugh Dickins in 2010) pointed out that this would result, at least temporarily, in two copies of the data in RAM: one (compressed for zcache) copy in tmem, and one copy in the swap cache. We wondered if this could be done differently, at least optionally. This patch allows tmem backends to instruct the frontswap code that this backend performs exclusive gets. Zcache2 already contains hooks to support this feature. Other backends are completely unaffected unless/until they are updated to support this feature. While it is not clear that exclusive gets are a performance win on all workloads at all times, this small patch allows for experimentation by backends. P.S. Let's not quibble about the naming of "get" vs "read" vs "load" etc. The naming is currently horribly inconsistent between cleancache and frontswap and existing tmem backends, so will need to be straightened out as a separate patch. "Get" is used by the tmem architecture spec, existing backends, and all documentation and presentation material so I am using it in this patch. Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
130 lines
3.0 KiB
C
130 lines
3.0 KiB
C
#ifndef _LINUX_FRONTSWAP_H
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#define _LINUX_FRONTSWAP_H
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#include <linux/swap.h>
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#include <linux/mm.h>
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#include <linux/bitops.h>
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struct frontswap_ops {
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void (*init)(unsigned);
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int (*store)(unsigned, pgoff_t, struct page *);
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int (*load)(unsigned, pgoff_t, struct page *);
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void (*invalidate_page)(unsigned, pgoff_t);
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void (*invalidate_area)(unsigned);
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};
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extern bool frontswap_enabled;
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extern struct frontswap_ops
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frontswap_register_ops(struct frontswap_ops *ops);
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extern void frontswap_shrink(unsigned long);
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extern unsigned long frontswap_curr_pages(void);
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extern void frontswap_writethrough(bool);
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#define FRONTSWAP_HAS_EXCLUSIVE_GETS
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extern void frontswap_tmem_exclusive_gets(bool);
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extern void __frontswap_init(unsigned type);
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extern int __frontswap_store(struct page *page);
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extern int __frontswap_load(struct page *page);
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extern void __frontswap_invalidate_page(unsigned, pgoff_t);
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extern void __frontswap_invalidate_area(unsigned);
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#ifdef CONFIG_FRONTSWAP
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static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
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{
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bool ret = false;
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if (frontswap_enabled && sis->frontswap_map)
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ret = test_bit(offset, sis->frontswap_map);
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return ret;
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}
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static inline void frontswap_set(struct swap_info_struct *sis, pgoff_t offset)
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{
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if (frontswap_enabled && sis->frontswap_map)
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set_bit(offset, sis->frontswap_map);
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}
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static inline void frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
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{
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if (frontswap_enabled && sis->frontswap_map)
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clear_bit(offset, sis->frontswap_map);
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}
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static inline void frontswap_map_set(struct swap_info_struct *p,
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unsigned long *map)
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{
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p->frontswap_map = map;
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}
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static inline unsigned long *frontswap_map_get(struct swap_info_struct *p)
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{
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return p->frontswap_map;
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}
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#else
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/* all inline routines become no-ops and all externs are ignored */
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#define frontswap_enabled (0)
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static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
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{
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return false;
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}
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static inline void frontswap_set(struct swap_info_struct *sis, pgoff_t offset)
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{
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}
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static inline void frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
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{
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}
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static inline void frontswap_map_set(struct swap_info_struct *p,
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unsigned long *map)
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{
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}
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static inline unsigned long *frontswap_map_get(struct swap_info_struct *p)
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{
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return NULL;
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}
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#endif
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static inline int frontswap_store(struct page *page)
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{
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int ret = -1;
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if (frontswap_enabled)
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ret = __frontswap_store(page);
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return ret;
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}
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static inline int frontswap_load(struct page *page)
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{
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int ret = -1;
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if (frontswap_enabled)
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ret = __frontswap_load(page);
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return ret;
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}
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static inline void frontswap_invalidate_page(unsigned type, pgoff_t offset)
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{
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if (frontswap_enabled)
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__frontswap_invalidate_page(type, offset);
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}
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static inline void frontswap_invalidate_area(unsigned type)
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{
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if (frontswap_enabled)
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__frontswap_invalidate_area(type);
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}
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static inline void frontswap_init(unsigned type)
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{
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if (frontswap_enabled)
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__frontswap_init(type);
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}
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#endif /* _LINUX_FRONTSWAP_H */
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