![Vlastimil Babka](/assets/img/avatar_default.png)
I have noticed that frontswap.h first declares "frontswap_enabled" as extern bool variable, and then overrides it with "#define frontswap_enabled (1)" for CONFIG_FRONTSWAP=Y or (0) when disabled. The bool variable isn't actually instantiated anywhere. This all looks like an unfinished attempt to make frontswap_enabled reflect whether a backend is instantiated. But in the current state, all frontswap hooks call unconditionally into frontswap.c just to check if frontswap_ops is non-NULL. This should at least be checked inline, but we can further eliminate the overhead when CONFIG_FRONTSWAP is enabled and no backend registered, using a static key that is initially disabled, and gets enabled only upon first backend registration. Thus, checks for "frontswap_enabled" are replaced with "frontswap_enabled()" wrapping the static key check. There are two exceptions: - xen's selfballoon_process() was testing frontswap_enabled in code guarded by #ifdef CONFIG_FRONTSWAP, which was effectively always true when reachable. The patch just removes this check. Using frontswap_enabled() does not sound correct here, as this can be true even without xen's own backend being registered. - in SYSCALL_DEFINE2(swapon), change the check to IS_ENABLED(CONFIG_FRONTSWAP) as it seems the bitmap allocation cannot currently be postponed until a backend is registered. This means that frontswap will still have some memory overhead by being configured, but without a backend. After the patch, we can expect that some functions in frontswap.c are called only when frontswap_ops is non-NULL. Change the checks there to VM_BUG_ONs. While at it, convert other BUG_ONs to VM_BUG_ONs as frontswap has been stable for some time. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/1463152235-9717-1-git-send-email-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
114 lines
2.8 KiB
C
114 lines
2.8 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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#include <linux/jump_label.h>
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struct frontswap_ops {
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void (*init)(unsigned); /* this swap type was just swapon'ed */
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int (*store)(unsigned, pgoff_t, struct page *); /* store a page */
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int (*load)(unsigned, pgoff_t, struct page *); /* load a page */
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void (*invalidate_page)(unsigned, pgoff_t); /* page no longer needed */
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void (*invalidate_area)(unsigned); /* swap type just swapoff'ed */
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struct frontswap_ops *next; /* private pointer to next ops */
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};
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extern void 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 bool __frontswap_test(struct swap_info_struct *, pgoff_t);
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extern void __frontswap_init(unsigned type, unsigned long *map);
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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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extern struct static_key_false frontswap_enabled_key;
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static inline bool frontswap_enabled(void)
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{
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return static_branch_unlikely(&frontswap_enabled_key);
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}
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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 __frontswap_test(sis, offset);
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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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static inline bool frontswap_enabled(void)
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{
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return false;
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}
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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_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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if (frontswap_enabled())
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return __frontswap_store(page);
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return -1;
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}
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static inline int frontswap_load(struct page *page)
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{
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if (frontswap_enabled())
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return __frontswap_load(page);
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return -1;
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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, unsigned long *map)
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{
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if (frontswap_enabled())
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__frontswap_init(type, map);
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}
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#endif /* _LINUX_FRONTSWAP_H */
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