Messages in this thread |  | | | Subject | Re: thp and memory barrier assumptions | | From | Peter Zijlstra <> | | Date | Thu, 26 Jul 2012 22:33:25 +0200 |
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On Thu, 2012-07-26 at 22:31 +0200, Peter Zijlstra wrote: > __do_huge_pmd_anonymous_page() contains: > > /* > * The spinlocking to take the lru_lock inside > * page_add_new_anon_rmap() acts as a full memory > * barrier to be sure clear_huge_page writes become > * visible after the set_pmd_at() write. > */ > page_add_new_anon_rmap(page, vma, haddr); > > > page_add_new_anon_rmap() doesn't look to actually do a LOCK+UNLOCK > except for unevictable pages. > > But even if it did do an unconditional LOCK+UNLOCK that doesn't make a > full memory barrier, see Documentation/memory-barriers.txt. > > In particular: > > *A = a; > LOCK > UNLOCK > *B = b; > > may occur as: > > LOCK, STORE *B, STORE *A, UNLOCK >
Also, what is that barrier() in handle_mm_fault() doing? And why doesn't it have a comment explaining that?
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