On 30/05/2024 08:49, Barry Song wrote: > On Wed, May 29, 2024 at 9:04 AM Chris Li <chrisl@xxxxxxxxxx> wrote: >> >> I am spinning a new version for this series to address two issues >> found in this series: >> >> 1) Oppo discovered a bug in the following line: >> + ci = si->cluster_info + tmp; >> Should be "tmp / SWAPFILE_CLUSTER" instead of "tmp". >> That is a serious bug but trivial to fix. >> >> 2) order 0 allocation currently blindly scans swap_map disregarding >> the cluster->order. Given enough order 0 swap allocations(close to the >> swap file size) the order 0 allocation head will eventually sweep >> across the whole swapfile and destroy other cluster order allocations. >> >> The short term fix is just skipping clusters that are already assigned >> to higher orders. >> >> In the long term, I want to unify the non-SSD to use clusters for >> locking and allocations as well, just try to follow the last >> allocation (less seeking) as much as possible. > > Hi Chris, > > I am sharing some new test results with you. This time, we used two > zRAM devices by modifying get_swap_pages(). > > zram0 -> dedicated for order-0 swpout > zram1 -> dedicated for order-4 swpout > > We allocate a generous amount of space for zRAM1 to ensure it never gets full > and always has ample free space. However, we found that Ryan's approach > does not perform well even in this straightforward scenario. Despite zRAM1 > having 80% of its space remaining, we still experience issues obtaining > contiguous swap slots and encounter a high swpout_fallback ratio. > > Sorry for the report, Ryan :-) No problem; clearly it needs to be fixed, and I'll help where I can. I'm pretty sure that this is due to fragmentation preventing clusters from being freed back to the free list. > > In contrast, with your patch, we consistently see the thp_swpout_fallback ratio > at 0%, indicating a significant improvement in the situation. Unless I've misunderstood something critical, Chris's change is just allowing a cpu to steal a block from another cpu's current cluster for that order. So it just takes longer (approx by a factor of the number of cpus in the system) to get to the state where fragmentation is causing fallbacks? As I said in the other thread, I think the more robust solution is to implement scanning for high order blocks. > > Although your patch still has issues supporting the mixing of order-0 and > order-4 pages in a swap device, it represents a significant improvement. > > I would be delighted to witness your approach advancing with Ying > Huang’s assistance. However, due to my current commitments, I > regret that I am unable to allocate time for debugging. > >> >> Chris >> >> >> >> On Fri, May 24, 2024 at 10:17 AM Chris Li <chrisl@xxxxxxxxxx> 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. That works well for PMD size THP, >>> but it has a serius fragmentation issue reported by Barry. >>> >>> https://lore.kernel.org/all/CAGsJ_4zAcJkuW016Cfi6wicRr8N9X+GJJhgMQdSMp+Ah+NSgNQ@xxxxxxxxxxxxxx/ >>> >>> The mTHP allocation failure rate raises to almost 100% after a few >>> hours in Barry's test run. >>> >>> 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. >>> >>> Address this by remember the swap allocation order in the cluster. >>> Keep track of the per order non full cluster list for later allocation. >>> >>> This greatly improve the sucess rate of the mTHP swap allocation. >>> While I am still waiting for Barry's test result. I paste Kairui's test >>> result here: >>> >>> I'm able to reproduce such an issue with a simple script (enabling all order of mthp): >>> >>> modprobe brd rd_nr=1 rd_size=$(( 10 * 1024 * 1024)) >>> swapoff -a >>> mkswap /dev/ram0 >>> swapon /dev/ram0 >>> >>> rmdir /sys/fs/cgroup/benchmark >>> mkdir -p /sys/fs/cgroup/benchmark >>> cd /sys/fs/cgroup/benchmark >>> echo 8G > memory.max >>> echo $$ > cgroup.procs >>> >>> memcached -u nobody -m 16384 -s /tmp/memcached.socket -a 0766 -t 32 -B binary & >>> >>> /usr/local/bin/memtier_benchmark -S /tmp/memcached.socket \ >>> -P memcache_binary -n allkeys --key-minimum=1 \ >>> --key-maximum=18000000 --key-pattern=P:P -c 1 -t 32 \ >>> --ratio 1:0 --pipeline 8 -d 1024 >>> >>> Before: >>> Totals 48805.63 0.00 0.00 5.26045 1.19100 38.91100 59.64700 51063.98 >>> After: >>> Totals 71098.84 0.00 0.00 3.60585 0.71100 26.36700 39.16700 74388.74 >>> >>> And the fallback ratio dropped by a lot: >>> Before: >>> hugepages-32kB/stats/anon_swpout_fallback:15997 >>> hugepages-32kB/stats/anon_swpout:18712 >>> hugepages-512kB/stats/anon_swpout_fallback:192 >>> hugepages-512kB/stats/anon_swpout:0 >>> hugepages-2048kB/stats/anon_swpout_fallback:2 >>> hugepages-2048kB/stats/anon_swpout:0 >>> hugepages-1024kB/stats/anon_swpout_fallback:0 >>> hugepages-1024kB/stats/anon_swpout:0 >>> hugepages-64kB/stats/anon_swpout_fallback:18246 >>> hugepages-64kB/stats/anon_swpout:17644 >>> hugepages-16kB/stats/anon_swpout_fallback:13701 >>> hugepages-16kB/stats/anon_swpout:18234 >>> hugepages-256kB/stats/anon_swpout_fallback:8642 >>> hugepages-256kB/stats/anon_swpout:93 >>> hugepages-128kB/stats/anon_swpout_fallback:21497 >>> hugepages-128kB/stats/anon_swpout:7596 >>> >>> (Still collecting more data, the success swpout was mostly done early, then the fallback began to increase, nearly 100% failure rate) >>> >>> After: >>> hugepages-32kB/stats/swpout:34445 >>> hugepages-32kB/stats/swpout_fallback:0 >>> hugepages-512kB/stats/swpout:1 >>> hugepages-512kB/stats/swpout_fallback:134 >>> hugepages-2048kB/stats/swpout:1 >>> hugepages-2048kB/stats/swpout_fallback:1 >>> hugepages-1024kB/stats/swpout:6 >>> hugepages-1024kB/stats/swpout_fallback:0 >>> hugepages-64kB/stats/swpout:35495 >>> hugepages-64kB/stats/swpout_fallback:0 >>> hugepages-16kB/stats/swpout:32441 >>> hugepages-16kB/stats/swpout_fallback:0 >>> hugepages-256kB/stats/swpout:2223 >>> hugepages-256kB/stats/swpout_fallback:6278 >>> hugepages-128kB/stats/swpout:29136 >>> hugepages-128kB/stats/swpout_fallback:52 >>> >>> Reported-by: Barry Song <21cnbao@xxxxxxxxx> >>> Tested-by: Kairui Song <kasong@xxxxxxxxxxx> >>> Signed-off-by: Chris Li <chrisl@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 | 18 ++-- >>> mm/swapfile.c | 252 +++++++++++++++++---------------------------------- >>> 2 files changed, 93 insertions(+), 177 deletions(-) >>> --- >>> base-commit: c65920c76a977c2b73c3a8b03b4c0c00cc1285ed >>> change-id: 20240523-swap-allocator-1534c480ece4 >>> >>> Best regards, >>> -- >>> Chris Li <chrisl@xxxxxxxxxx> >>> > > Thanks > Barry
