Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > On Thu, 11 Aug 2022 12:13:29 -0400 Peter Xu <peterx@xxxxxxxxxx> wrote: > >> When page migration happens, we always ignore the young/dirty bit settings >> in the old pgtable, and marking the page as old in the new page table using >> either pte_mkold() or pmd_mkold(), and keeping the pte clean. >> >> That's fine from functional-wise, but that's not friendly to page reclaim >> because the moving page can be actively accessed within the procedure. Not >> to mention hardware setting the young bit can bring quite some overhead on >> some systems, e.g. x86_64 needs a few hundreds nanoseconds to set the bit. >> The same slowdown problem to dirty bits when the memory is first written >> after page migration happened. >> >> Actually we can easily remember the A/D bit configuration and recover the >> information after the page is migrated. To achieve it, define a new set of >> bits in the migration swap offset field to cache the A/D bits for old pte. >> Then when removing/recovering the migration entry, we can recover the A/D >> bits even if the page changed. >> >> One thing to mention is that here we used max_swapfile_size() to detect how >> many swp offset bits we have, and we'll only enable this feature if we know >> the swp offset is big enough to store both the PFN value and the A/D bits. >> Otherwise the A/D bits are dropped like before. >> > > There was some discussion over v3 of this patch, but none over v4. > > Can people please review this patch series so we can get moving with it? Most discussions over v3 are for migrate_device.c code. There are some bugs and they have been fixed by Alistair via [1]. This patch itself is good. Sorry for bothering. Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx> [1] https://lore.kernel.org/linux-mm/9f801e9d8d830408f2ca27821f606e09aa856899.1662078528.git-series.apopple@xxxxxxxxxx/ Best Regards, Huang, Ying
