On (06/03/16 10:29), Sergey Senozhatsky wrote:
> > if (allocstall == curr_allocstall && swap != 0) {
> > if (!__collapse_huge_page_swapin(mm, vma, address, pmd)) {
> > {
> > : if (ret & VM_FAULT_RETRY) {
> > : down_read(&mm->mmap_sem);
> > : ^^^^^^^^^
>
> oh... it's in a loop
>
> for (_address = address; _address < address +
> HPAGE_PMD_NR*PAGE_SIZE;
> pte++, _address += PAGE_SIZE) {
> ret = do_swap_page()
> if (ret & VM_FAULT_RETRY) {
> down_read(&mm->mmap_sem);
> ^^^^^^^^^
> ...
> }
> }
>
> so there can be multiple sem->count++ in __collapse_huge_page_swapin(),
> and you don't know how many sem->count-- you need to do later? is this
> correct or am I hallucinating?
No, I was wrong, sorry for the noise.
it's getting unlocked in
__collapse_huge_page_swapin()
do_swap_page()
lock_page_or_retry()
if (flags & FAULT_FLAG_ALLOW_RETRY)
up_read(&mm->mmap_sem);
return VM_FAULT_RETRY
-ss
