On Tue, Mar 8, 2011 at 9:58 PM, Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote: > On Tue, Mar 08, 2011 at 04:21:15AM -0800, Michel Lespinasse wrote: >> On Tue, Mar 08, 2011 at 12:32:45PM +0100, Andrea Arcangeli wrote: >> > I only run some basic testing, please review. I seen no reason to >> > return "referenced = 0" if the pmd is still splitting. So I let it go >> > ahead now and test_and_set_bit the accessed bit even on a splitting >> > pmd. After all the tlb miss could still activate the young bit on a >> > pmd while it's in splitting state. There's no check for splitting in >> > the pmdp_clear_flush_young. The secondary mmu has no secondary spte >> > mapped while it's set to splitting so it shouldn't matter for it if we >> > clear the young bit (and new secondary mmu page faults will wait on >> > splitting to clear and __split_huge_page_map to finish before going >> > ahead creating new secondary sptes with 4k granularity). >> >> Agree, the pmd_trans_splitting check didn't seem necessary. >> >> Thanks for the patch, looks fine, I only have a couple nitpicks regarding >> code comments: >> > > Ok, updated comments... thanks for the quick review. Try #2: > > === > Subject: thp: fix page_referenced to modify mapcount/vm_flags only if page is found > > From: Andrea Arcangeli <aarcange@xxxxxxxxxx> > > When vmscan.c calls page_referenced, if an anon page was created before a > process forked, rmap will search for it in both of the processes, even though > one of them might have since broken COW. If the child process mlocks the vma > where the COWed page belongs to, page_referenced() running on the page mapped > by the parent would lead to *vm_flags getting VM_LOCKED set erroneously (leading > to the references on the parent page being ignored and evicting the parent page > too early). > > *mapcount would also be decremented by page_referenced_one even if the page > wasn't found by page_check_address. > > This also let pmdp_clear_flush_young_notify() go ahead on a > pmd_trans_splitting() pmd. We hold the page_table_lock so > __split_huge_page_map() must wait the pmdp_clear_flush_young_notify() to > complete before it can modify the pmd. The pmd is also still mapped in userland > so the young bit may materialize through a tlb miss before split_huge_page_map > runs. This will provide a more accurate page_referenced() behavior during > split_huge_page(). > > Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> > Reported-by: Michel Lespinasse <walken@xxxxxxxxxx> > Reviewed-by: Michel Lespinasse <walken@xxxxxxxxxx> Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx> -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>