On Thu, Sep 12, 2024 at 10:34 AM Vlastimil Babka <vbabka@xxxxxxx> wrote: > > > "If the partial slab becomes an empty slab after freeing up the > > object, it will be left in its current list if the number of partial > > slabs for the concerned node is within the limits (i.e < slab cache’s > > min_partial). This applies to both slabs belonging to a per-cpu > > partial slab list and slabs belonging to a per-node partial slab list. > > If the number of partial slabs are outside the limit (i.e >= slab > > cache’s min partial) then the newly available empty slab is freed and > > is removed from the corresponding partial slab list." > > > > The part that seems wrong to me here is the statement that this > > applies to the per-CPU partial list. Based on the code in __slab_free, > > it looks like it cannot reach the slab_empty label for a slab that is > > on the per-CPU partial list. > > > > (I know that an empty per-CPU partial slab can be freed when the list > > overflows or via shrinking, the question is about the slab being freed > > directly by __slab_free.) > > > > Is the article wrong with regards to this case? Or did this behavior > > change recently (I failed found any traces of this)? > > I don't think the behavior changed recently in this aspect, only in some > other details like tracking on_node_partial with a page flag for better > performance, and slabs on per-cpu partial list are no longer frozen. > > I think the paragraph you quoted can be interpreted together with this part > of the preceding one: "However while putting this partial slab on a per-cpu > partial slab list if it is found that the per-cpu partial slab list is > already full, then all slabs from the per-cpu partial slab list are unfrozen > i.e they are moved to a per-node partial slab list and this new partial slab > is put on the per-cpu partial slab list." > > So while flushing the per-cpu partial list, the per-cpu partial slabs are > moved to per-node partial list, and when __put_partials() finds some of them > are empty, it applies the same s->min_partial threshold to decide whether to > keep them in node partial list or free them. So in that sense "This applies > to both..." part is correct, although as you say it cannot immediately > affect a slab on partial list we are freeing to. Ack, thank you for the response!
