On Tue, Mar 12, 2024 at 6:26 AM Chris Li <chrisl@xxxxxxxxxx> wrote: > > Very deep RB tree requires rebalance at times. That > contributes to the zswap fault latencies. Xarray does not > need to perform tree rebalance. Replacing RB tree to xarray > can have some small performance gain. > > One small difference is that xarray insert might fail with > ENOMEM, while RB tree insert does not allocate additional > memory. > > The zswap_entry size will reduce a bit due to removing the > RB node, which has two pointers and a color field. Xarray > store the pointer in the xarray tree rather than the > zswap_entry. Every entry has one pointer from the xarray > tree. Overall, switching to xarray should save some memory, > if the swap entries are densely packed. > > Notice the zswap_rb_search and zswap_rb_insert always > followed by zswap_rb_erase. Use xa_erase and xa_store > directly. That saves one tree lookup as well. > > Remove zswap_invalidate_entry due to no need to call > zswap_rb_erase any more. Use zswap_free_entry instead. > > The "struct zswap_tree" has been replaced by "struct xarray". > The tree spin lock has transferred to the xarray lock. > > Run the kernel build testing 10 times for each version, averages: > (memory.max=2GB, zswap shrinker and writeback enabled, > one 50GB swapfile, 24 HT core, 32 jobs) > > mm-9a0181a3710eb xarray v5 > user 3532.385 3535.658 > sys 536.231 530.083 > real 200.431 200.176 > > --- > > > Signed-off-by: Chris Li <chrisl@xxxxxxxxxx> > --- > Changes in v5: > - Remove zswap_xa_insert(), call xa_store and xa_erase directly. > - Remove zswap_reject_xarray_fail. > - Link to v4: https://lore.kernel.org/r/20240304-zswap-xarray-v4-1-c4b45670cc30@xxxxxxxxxx > > Changes in v4: > - Remove zswap_xa_search_and_earse, use xa_erase directly. > - Move charge of objcg after zswap_xa_insert. > - Avoid erase old entry on insert fail error path. > - Remove not needed swap_zswap_tree change > - Link to v3: https://lore.kernel.org/r/20240302-zswap-xarray-v3-1-5900252f2302@xxxxxxxxxx > > Changes in v3: > - Use xa_cmpxchg instead of zswap_xa_search_and_delete in zswap_writeback_entry. > - Use xa_store in zswap_xa_insert directly. Reduce the scope of spinlock. > - Fix xa_store error handling for same page fill case. > - Link to v2: https://lore.kernel.org/r/20240229-zswap-xarray-v2-1-e50284dfcdb1@xxxxxxxxxx > > Changes in v2: > - Replace struct zswap_tree with struct xarray. > - Remove zswap_tree spinlock, use xarray lock instead. > - Fold zswap_rb_erase() into zswap_xa_search_and_delete() and zswap_xa_insert(). > - Delete zswap_invalidate_entry(), use zswap_free_entry() instead. > - Link to v1: https://lore.kernel.org/r/20240117-zswap-xarray-v1-0-6daa86c08fae@xxxxxxxxxx > --- > mm/zswap.c | 166 +++++++++++++++---------------------------------------------- > 1 file changed, 41 insertions(+), 125 deletions(-) It appears to be a suitable figure. And LGTM, Reviewed-by: Barry Song <baohua@xxxxxxxxxx> Thanks Barry
