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Commit 7a9cdebd authored by Linus Torvalds's avatar Linus Torvalds
Browse files

mm: get rid of vmacache_flush_all() entirely 



Jann Horn points out that the vmacache_flush_all() function is not only
potentially expensive, it's buggy too.  It also happens to be entirely
unnecessary, because the sequence number overflow case can be avoided by
simply making the sequence number be 64-bit.  That doesn't even grow the
data structures in question, because the other adjacent fields are
already 64-bit.

So simplify the whole thing by just making the sequence number overflow
case go away entirely, which gets rid of all the complications and makes
the code faster too.  Win-win.

[ Oleg Nesterov points out that the VMACACHE_FULL_FLUSHES statistics
  also just goes away entirely with this ]

Reported-by: default avatarJann Horn <jannh@google.com>
Suggested-by: default avatarWill Deacon <will.deacon@arm.com>
Acked-by: default avatarDavidlohr Bueso <dave@stgolabs.net>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: stable@kernel.org
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 54eda9df

include/linux/mm_types.h

+1 −1
Original line number Diff line number Diff line
@@ -341,7 +341,7 @@ struct mm_struct { 
	struct {

		struct vm_area_struct *mmap;		/* list of VMAs */

		struct rb_root mm_rb;

		u32 vmacache_seqnum;                   /* per-thread vmacache */

		u64 vmacache_seqnum;                   /* per-thread vmacache */

#ifdef CONFIG_MMU

		unsigned long (*get_unmapped_area) (struct file *filp,

				unsigned long addr, unsigned long len,

include/linux/mm_types_task.h

+1 −1
Original line number Diff line number Diff line
@@ -32,7 +32,7 @@ 
#define VMACACHE_MASK (VMACACHE_SIZE - 1)



struct vmacache {

	u32 seqnum;

	u64 seqnum;

	struct vm_area_struct *vmas[VMACACHE_SIZE];

};

include/linux/vm_event_item.h

+0 −1
Original line number Diff line number Diff line
@@ -105,7 +105,6 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, 
#ifdef CONFIG_DEBUG_VM_VMACACHE

		VMACACHE_FIND_CALLS,

		VMACACHE_FIND_HITS,

		VMACACHE_FULL_FLUSHES,

#endif

#ifdef CONFIG_SWAP

		SWAP_RA,

include/linux/vmacache.h

+0 −5
Original line number Diff line number Diff line
@@ -10,7 +10,6 @@ static inline void vmacache_flush(struct task_struct *tsk) 
	memset(tsk->vmacache.vmas, 0, sizeof(tsk->vmacache.vmas));

}



extern void vmacache_flush_all(struct mm_struct *mm);

extern void vmacache_update(unsigned long addr, struct vm_area_struct *newvma);

extern struct vm_area_struct *vmacache_find(struct mm_struct *mm,

						    unsigned long addr);
@@ -24,10 +23,6 @@ extern struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm, 
static inline void vmacache_invalidate(struct mm_struct *mm)

{

	mm->vmacache_seqnum++;



	/* deal with overflows */

	if (unlikely(mm->vmacache_seqnum == 0))

		vmacache_flush_all(mm);

}



#endif /* __LINUX_VMACACHE_H */

mm/debug.c

+2 −2
Original line number Diff line number Diff line
@@ -114,7 +114,7 @@ EXPORT_SYMBOL(dump_vma); 


void dump_mm(const struct mm_struct *mm)

{

	pr_emerg("mm %px mmap %px seqnum %d task_size %lu\n"

	pr_emerg("mm %px mmap %px seqnum %llu task_size %lu\n"

#ifdef CONFIG_MMU

		"get_unmapped_area %px\n"

#endif
@@ -142,7 +142,7 @@ void dump_mm(const struct mm_struct *mm) 
		"tlb_flush_pending %d\n"

		"def_flags: %#lx(%pGv)\n",



		mm, mm->mmap, mm->vmacache_seqnum, mm->task_size,

		mm, mm->mmap, (long long) mm->vmacache_seqnum, mm->task_size,

#ifdef CONFIG_MMU

		mm->get_unmapped_area,

#endif