Hi Manfred, I had few side conversations with Andrew and he recommend I check with you. I have been trying to track down a fragmentation problem with slab-64, while simulating scsi-debug disks. To narrow it down further, I created size-40 slab and now I see fragmentation on this slab. I have 2 issues: 1) After the machine boot, I see that size-40 slab is already fragmented. size-40 2633 11468 64 61 1 : tunables 120 60 8 : slabdata 188 188 0 2) I simulate 512 disks using scsi-debug, I see that size-40 "inuse" objects increasing, but "active" objects are increasing very rapidly. At no point, I see all the active objects are in use. I am not sure why ? I expected to see few (hundreds) active objects more, but not this many. At the end of the test, slab-40 is so heavily fragmented, only one object is in use per slab (holding up all the slabs). I run out of lowmem slowly. I modified "crash" kmem command to dump all the slabs in the cache. I am attaching the output. I am wondering why we are not filling up partial slabs, before allocating new ones ? slab-40 (output every 1 sec while running test): size-40 2633 11468 64 61 1 : tunables 120 60 8 : slabdata 188 188 0 size-40 2633 11468 64 61 1 : tunables 120 60 8 : slabdata 188 188 0 size-40 2633 11468 64 61 1 : tunables 120 60 8 : slabdata 188 188 0 size-40 2633 11468 64 61 1 : tunables 120 60 8 : slabdata 188 188 0 size-40 4457 27084 64 61 1 : tunables 120 60 ====> test start 8 : slabdata 444 444 0 size-40 7685 59292 64 61 1 : tunables 120 60 8 : slabdata 972 972 0 size-40 10761 89548 64 61 1 : tunables 120 60 8 : slabdata 1468 1468 0 size-40 13589 119316 64 61 1 : tunables 120 60 8 : slabdata 1956 1956 0 size-40 16717 149084 64 61 1 : tunables 120 60 8 : slabdata 2444 2444 0 size-40 19929 180316 64 61 1 : tunables 120 60 8 : slabdata 2956 2956 0 size-40 22961 211548 64 61 1 : tunables 120 60 8 : slabdata 3468 3468 0 size-40 25969 241316 64 61 1 : tunables 120 60 8 : slabdata 3956 3956 0 size-40 27841 260348 64 61 1 : tunables 120 60 8 : slabdata 4268 4268 0 size-40 27841 260348 64 61 1 : tunables 120 60 8 : slabdata 4268 4268 0 size-40 27813 260348 64 61 1 : tunables 120 60 8 : slabdata 4268 4268 0 size-40 27726 260348 64 61 1 : tunables 120 60 8 : slabdata 4268 4268 0 size-40 27717 260348 64 61 1 : tunables 120 60 8 : slabdata 4268 4268 0 size-40 27698 260348 64 61 1 : tunables 120 60 8 : slabdata 4268 4268 0 size-40 27690 260348 64 61 1 : tunables 120 60 8 : slabdata 4268 4268 0 size-40 27680 260348 64 61 1 : tunables 120 60 8 : slabdata 4268 4268 0 size-40 27676 260348 64 61 1 : tunables 120 60 8 : slabdata 4268 4268 0 Thanks, Badari