On 6/19/18 3:02 AM, Peter Zijlstra wrote:
On Tue, Jun 19, 2018 at 07:34:16AM +0800, Yang Shi wrote:diff --git a/mm/mmap.c b/mm/mmap.c index fc41c05..e84f80c 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2686,6 +2686,141 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma, return __split_vma(mm, vma, addr, new_below); }+/* Consider PUD size or 1GB mapping as large mapping */+#ifdef HPAGE_PUD_SIZE +#define LARGE_MAP_THRESH HPAGE_PUD_SIZE +#else +#define LARGE_MAP_THRESH (1 * 1024 * 1024 * 1024) +#endif + +/* Unmap large mapping early with acquiring read mmap_sem */ +static int do_munmap_zap_early(struct mm_struct *mm, unsigned long start, + size_t len, struct list_head *uf) +{ + unsigned long end = 0; + struct vm_area_struct *vma = NULL, *prev, *last, *tmp; + bool success = false; + int ret = 0; + + if ((offset_in_page(start)) || start > TASK_SIZE || len > TASK_SIZE - start) + return -EINVAL; + + len = (PAGE_ALIGN(len)); + if (len == 0) + return -EINVAL; + + /* Just deal with uf in regular path */ + if (unlikely(uf)) + goto regular_path; + + if (len >= LARGE_MAP_THRESH) { + down_read(&mm->mmap_sem); + vma = find_vma(mm, start); + if (!vma) { + up_read(&mm->mmap_sem); + return 0; + } + + prev = vma->vm_prev; + + end = start + len; + if (vma->vm_start > end) { + up_read(&mm->mmap_sem); + return 0; + } + + if (start > vma->vm_start) { + int error; + + if (end < vma->vm_end && + mm->map_count > sysctl_max_map_count) { + up_read(&mm->mmap_sem); + return -ENOMEM; + } + + error = __split_vma(mm, vma, start, 0); + if (error) { + up_read(&mm->mmap_sem); + return error; + } + prev = vma; + } + + last = find_vma(mm, end); + if (last && end > last->vm_start) { + int error = __split_vma(mm, last, end, 1); + + if (error) { + up_read(&mm->mmap_sem); + return error; + } + } + vma = prev ? prev->vm_next : mm->mmap;Hold up, two things: you having to copy most of do_munmap() didn't seem to suggest a helper function? And second, since when are we allowed to
Yes, they will be extracted into a helper function in the next version. May bad, I don't think it is allowed. We could reform this to: acquire write mmap_sem vma lookup (split vmas) release write mmap_sem acquire read mmap_sem zap pages release read mmap_sem I'm supposed this is safe as what Michal said before. Thanks, Yang
split VMAs under a read lock?
