6b4ebc3a90
For single threaded workloads, we can avoid flushing and iterating through the entire list of tasks, making the whole function a lot faster, requiring only a single atomic read for the mm_users. Signed-off-by: Davidlohr Bueso <davidlohr@hp.com> Suggested-by: Oleg Nesterov <oleg@redhat.com> Cc: Aswin Chandramouleeswaran <aswin@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
133 lines
3.1 KiB
C
133 lines
3.1 KiB
C
/*
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* Copyright (C) 2014 Davidlohr Bueso.
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*/
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <linux/vmacache.h>
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/*
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* Flush vma caches for threads that share a given mm.
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*
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* The operation is safe because the caller holds the mmap_sem
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* exclusively and other threads accessing the vma cache will
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* have mmap_sem held at least for read, so no extra locking
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* is required to maintain the vma cache.
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*/
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void vmacache_flush_all(struct mm_struct *mm)
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{
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struct task_struct *g, *p;
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/*
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* Single threaded tasks need not iterate the entire
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* list of process. We can avoid the flushing as well
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* since the mm's seqnum was increased and don't have
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* to worry about other threads' seqnum. Current's
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* flush will occur upon the next lookup.
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*/
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if (atomic_read(&mm->mm_users) == 1)
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return;
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rcu_read_lock();
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for_each_process_thread(g, p) {
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/*
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* Only flush the vmacache pointers as the
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* mm seqnum is already set and curr's will
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* be set upon invalidation when the next
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* lookup is done.
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*/
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if (mm == p->mm)
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vmacache_flush(p);
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}
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rcu_read_unlock();
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}
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/*
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* This task may be accessing a foreign mm via (for example)
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* get_user_pages()->find_vma(). The vmacache is task-local and this
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* task's vmacache pertains to a different mm (ie, its own). There is
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* nothing we can do here.
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*
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* Also handle the case where a kernel thread has adopted this mm via use_mm().
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* That kernel thread's vmacache is not applicable to this mm.
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*/
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static bool vmacache_valid_mm(struct mm_struct *mm)
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{
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return current->mm == mm && !(current->flags & PF_KTHREAD);
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}
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void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
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{
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if (vmacache_valid_mm(newvma->vm_mm))
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current->vmacache[VMACACHE_HASH(addr)] = newvma;
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}
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static bool vmacache_valid(struct mm_struct *mm)
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{
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struct task_struct *curr;
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if (!vmacache_valid_mm(mm))
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return false;
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curr = current;
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if (mm->vmacache_seqnum != curr->vmacache_seqnum) {
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/*
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* First attempt will always be invalid, initialize
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* the new cache for this task here.
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*/
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curr->vmacache_seqnum = mm->vmacache_seqnum;
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vmacache_flush(curr);
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return false;
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}
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return true;
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}
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struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
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{
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int i;
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if (!vmacache_valid(mm))
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return NULL;
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count_vm_vmacache_event(VMACACHE_FIND_CALLS);
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for (i = 0; i < VMACACHE_SIZE; i++) {
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struct vm_area_struct *vma = current->vmacache[i];
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if (!vma)
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continue;
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if (WARN_ON_ONCE(vma->vm_mm != mm))
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break;
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if (vma->vm_start <= addr && vma->vm_end > addr) {
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count_vm_vmacache_event(VMACACHE_FIND_HITS);
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return vma;
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}
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}
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return NULL;
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}
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#ifndef CONFIG_MMU
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struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
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unsigned long start,
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unsigned long end)
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{
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int i;
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if (!vmacache_valid(mm))
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return NULL;
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count_vm_vmacache_event(VMACACHE_FIND_CALLS);
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for (i = 0; i < VMACACHE_SIZE; i++) {
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struct vm_area_struct *vma = current->vmacache[i];
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if (vma && vma->vm_start == start && vma->vm_end == end) {
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count_vm_vmacache_event(VMACACHE_FIND_HITS);
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return vma;
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}
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}
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return NULL;
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}
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#endif
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