Hello, On Tue, Aug 01, 2017 at 02:56:17PM +0900, Minchan Kim wrote: > CPU0 CPU1 CPU2 CPU3 > ---- ---- ---- ---- > Write the same > value on page > > [cache PTE as > dirty in TLB] > > MADV_FREE > pte_mkclean() > > 4 > clear_refs > pte_wrprotect() > > write_protect_page() > [ success, no flush ] > > pages_indentical() > [ ok ] > > Write to page > different value > > [Ok, using stale > PTE] > > replace_page() > > Later, CPU1, CPU2 and CPU3 would flush the TLB, but that is too late. CPU0 > already wrote on the page, but KSM ignored this write, and it got lost. > " > > In above scenario, MADV_FREE is fixed by changing TLB batching API > including [set|clear]_tlb_flush_pending. Remained thing is soft-dirty part. > > This patch changes soft-dirty uses TLB batching API instead of flush_tlb_mm > and KSM checks pending TLB flush by using mm_tlb_flush_pending so that > it will flush TLB to avoid data lost if there are other parallel threads > pending TLB flush. > > [1] http://lkml.kernel.org/r/[email protected] > > Note: > I failed to reproduce this problem through Nadav's test program which > need to tune timing in my system speed so didn't confirm it work. > Nadav, Could you test this patch on your test machine?
Reviewed-by: Andrea Arcangeli <[email protected]>
