On 4/12/24 1:20 PM, Vlastimil Babka wrote: > On 4/12/24 7:29 PM, Jianfeng Wang wrote: >> >> >> On 4/12/24 12:48 AM, Vlastimil Babka wrote: >>> On 4/11/24 7:02 PM, Christoph Lameter (Ampere) wrote: >>>> On Thu, 11 Apr 2024, Jianfeng Wang wrote: >>>> >>>>> So, the fix is to limit the number of slabs to scan in >>>>> count_partial(), and output an approximated result if the list is too >>>>> long. Default to 10000 which should be enough for most sane cases. >>>> >>>> >>>> That is a creative approach. The problem though is that objects on the >>>> partial lists are kind of sorted. The partial slabs with only a few >>>> objects available are at the start of the list so that allocations cause >>>> them to be removed from the partial list fast. Full slabs do not need to >>>> be tracked on any list. >>>> >>>> The partial slabs with few objects are put at the end of the partial list >>>> in the hope that the few objects remaining will also be freed which would >>>> allow the freeing of the slab folio. >>>> >>>> So the object density may be higher at the beginning of the list. >>>> >>>> kmem_cache_shrink() will explicitly sort the partial lists to put the >>>> partial pages in that order. >>>> >>>> Can you run some tests showing the difference between the estimation and >>>> the real count? >> >> Yes. >> On a server with one NUMA node, I create a case that uses many dentry objects. > > Could you describe in more detail how do you make dentry cache to grow such > a large partial slabs list? Thanks. > I utilized the fact that creating a folder will create a new dentry object; deleting a folder will delete all its sub-folder's dentry objects. Then, I started to create N folders, while each folder has M empty sub-folders. Assuming that these operations would consume a large number of dentry objects in the sequential order. Their slabs were very likely to be full slabs. After all folders were created, I deleted a subset of the N folders (i.e., one out of every two folders). This would create many holes, which turned a subset of full slabs into partial slabs.
