On 19/06/2024 10:20, Chris Li wrote: > This is the short term solutiolns "swap cluster order" listed > in my "Swap Abstraction" discussion slice 8 in the recent > LSF/MM conference. > > When commit 845982eb264bc "mm: swap: allow storage of all mTHP > orders" is introduced, it only allocates the mTHP swap entries > from new empty cluster list. It has a fragmentation issue > reported by Barry. > > https://lore.kernel.org/all/CAGsJ_4zAcJkuW016Cfi6wicRr8N9X+GJJhgMQdSMp+Ah+NSgNQ@xxxxxxxxxxxxxx/ > > The reason is that all the empty cluster has been exhausted while > there are planty of free swap entries to in the cluster that is > not 100% free. > > Remember the swap allocation order in the cluster. > Keep track of the per order non full cluster list for later allocation. > > User impact: For users that allocate and free mix order mTHP swapping, > It greatly improves the success rate of the mTHP swap allocation after the > initial phase. > > Barry provides a test program to show the effect: > https://lore.kernel.org/linux-mm/20240615084714.37499-1-21cnbao@xxxxxxxxx/ > > Without: > $ mthp-swapout > Iteration 1: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 2: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 3: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 4: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 5: swpout inc: 110, swpout fallback inc: 117, Fallback percentage: 51.54% > Iteration 6: swpout inc: 0, swpout fallback inc: 230, Fallback percentage: 100.00% > Iteration 7: swpout inc: 0, swpout fallback inc: 229, Fallback percentage: 100.00% > Iteration 8: swpout inc: 0, swpout fallback inc: 223, Fallback percentage: 100.00% > Iteration 9: swpout inc: 0, swpout fallback inc: 224, Fallback percentage: 100.00% > Iteration 10: swpout inc: 0, swpout fallback inc: 216, Fallback percentage: 100.00% > Iteration 11: swpout inc: 0, swpout fallback inc: 212, Fallback percentage: 100.00% > Iteration 12: swpout inc: 0, swpout fallback inc: 224, Fallback percentage: 100.00% > Iteration 13: swpout inc: 0, swpout fallback inc: 214, Fallback percentage: 100.00% > > $ mthp-swapout -s > Iteration 1: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 2: swpout inc: 227, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 3: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 4: swpout inc: 224, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 5: swpout inc: 33, swpout fallback inc: 197, Fallback percentage: 85.65% > Iteration 6: swpout inc: 0, swpout fallback inc: 229, Fallback percentage: 100.00% > Iteration 7: swpout inc: 0, swpout fallback inc: 223, Fallback percentage: 100.00% > Iteration 8: swpout inc: 0, swpout fallback inc: 219, Fallback percentage: 100.00% > Iteration 9: swpout inc: 0, swpout fallback inc: 212, Fallback percentage: 100.00% > > With: > $ mthp-swapout > Iteration 1: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 2: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 3: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 4: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 5: swpout inc: 227, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 6: swpout inc: 230, swpout fallback inc: 0, Fallback percentage: 0.00% > ... > Iteration 94: swpout inc: 224, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 95: swpout inc: 221, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 96: swpout inc: 229, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 97: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 98: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 99: swpout inc: 223, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 100: swpout inc: 224, swpout fallback inc: 0, Fallback percentage: 0.00% > > $ mthp-swapout -s > Iteration 1: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 2: swpout inc: 227, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 3: swpout inc: 222, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 4: swpout inc: 224, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 5: swpout inc: 230, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 6: swpout inc: 229, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 7: swpout inc: 223, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 8: swpout inc: 219, swpout fallback inc: 0, Fallback percentage: 0.00% > ... > Iteration 94: swpout inc: 223, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 95: swpout inc: 212, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 96: swpout inc: 220, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 97: swpout inc: 220, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 98: swpout inc: 216, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 99: swpout inc: 223, swpout fallback inc: 0, Fallback percentage: 0.00% > Iteration 100: swpout inc: 225, swpout fallback inc: 0, Fallback percentage: 0.00% Excellent! > > Reported-by: Barry Song <21cnbao@xxxxxxxxx> > Signed-off-by: Chris Li <chrisl@xxxxxxxxxx> > --- > Changes in v3: > - Using V1 as base. > - Rename "next" to "list" for the list field, suggested by Ying. > - Update comment for the locking rules for cluster fields and list, > suggested by Ying. > - Allocate from the nonfull list before attempting free list, suggested > by Kairui. Sorry I didn't follow this original conversation. But the original intent of having a per-cpu current cluster was to prevent interleving pages from multiple processes and therefore optimize IO. See commit ebc2a1a69111 ("swap: make cluster allocation per-cpu"). I wonder if this change could lead to a swap performance regression in the common order-0 case? Thanks, Ryan > - Link to v2: https://lore.kernel.org/r/20240614-swap-allocator-v2-0-2a513b4a7f2f@xxxxxxxxxx > > Changes in v2: > - Abandoned. > - Link to v1: https://lore.kernel.org/r/20240524-swap-allocator-v1-0-47861b423b26@xxxxxxxxxx > > --- > Chris Li (2): > mm: swap: swap cluster switch to double link list > mm: swap: mTHP allocate swap entries from nonfull list > > include/linux/swap.h | 30 +++---- > mm/swapfile.c | 248 +++++++++++++++++---------------------------------- > 2 files changed, 95 insertions(+), 183 deletions(-) > --- > base-commit: 19b8422c5bd56fb5e7085995801c6543a98bda1f > change-id: 20240523-swap-allocator-1534c480ece4 > > Best regards,
