From: Hui Zhu When kmem_cache_alloc_bulk() allocates multiple objects, the post-alloc hook __memcg_slab_post_alloc_hook() previously charged memcg one object at a time, even though consecutive objects may reside on slabs backed by the same pgdat node. Batch the memcg charging by scanning ahead from the current position to find a contiguous run of objects whose slabs share the same pgdat, then issue a single __obj_cgroup_charge() / __consume_obj_stock() call for the entire run. The per-object obj_ext assignment loop is preserved as-is since it cannot be further collapsed. This implements the TODO comment left in commit bc730030f956 ("memcg: combine slab obj stock charging and accounting"). The existing error-recovery contract is unchanged: if size == 1 then memcg_alloc_abort_single() will free the sole object, and for larger bulk allocations kmem_cache_free_bulk() will uncharge any objects that were already charged before the failure. Benchmark using kmem_cache_alloc_bulk() with SLAB_ACCOUNT (iters=100000): bulk=32 before: 215 ns/object after: 174 ns/object (-19%) bulk=1 before: 344 ns/object after: 335 ns/object ( ~) No measurable regression for bulk=1, as expected. Signed-off-by: Hui Zhu --- Changelog: v3: Update base from "mm-unstable" to "mm-stable". v2: According to the comments in [1], add code to handle the integer overflow issue. [1] https://sashiko.dev/#/patchset/20260316084839.1342163-1-hui.zhu%40linux.dev mm/memcontrol.c | 77 +++++++++++++++++++++++++++++++++++++------------ 1 file changed, 58 insertions(+), 19 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 051b82ebf371..3159bf39e060 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3277,51 +3277,90 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, return false; } - for (i = 0; i < size; i++) { + for (i = 0; i < size; ) { unsigned long obj_exts; struct slabobj_ext *obj_ext; struct obj_stock_pcp *stock; + struct pglist_data *pgdat; + int batch_bytes; + size_t run_len = 0; + size_t j; + size_t max_size; + bool skip_next = false; slab = virt_to_slab(p[i]); if (!slab_obj_exts(slab) && alloc_slab_obj_exts(slab, s, flags, false)) { + i++; continue; } + pgdat = slab_pgdat(slab); + run_len = 1; + + /* + * The value of batch_bytes must not exceed + * (INT_MAX - PAGE_SIZE) to prevent integer overflow in + * the final accumulation performed by __account_obj_stock(). + */ + max_size = min((size_t)((INT_MAX - PAGE_SIZE) / obj_size), + size); + + for (j = i + 1; j < max_size; j++) { + struct slab *slab_j = virt_to_slab(p[j]); + + if (slab_pgdat(slab_j) != pgdat) + break; + + if (!slab_obj_exts(slab_j) && + alloc_slab_obj_exts(slab_j, s, flags, false)) { + skip_next = true; + break; + } + + run_len++; + } + /* - * if we fail and size is 1, memcg_alloc_abort_single() will + * If we fail and size is 1, memcg_alloc_abort_single() will * just free the object, which is ok as we have not assigned - * objcg to its obj_ext yet - * - * for larger sizes, kmem_cache_free_bulk() will uncharge - * any objects that were already charged and obj_ext assigned + * objcg to its obj_ext yet. * - * TODO: we could batch this until slab_pgdat(slab) changes - * between iterations, with a more complicated undo + * For larger sizes, kmem_cache_free_bulk() will uncharge + * any objects that were already charged and obj_ext assigned. */ + batch_bytes = obj_size * run_len; stock = trylock_stock(); - if (!stock || !__consume_obj_stock(objcg, stock, obj_size)) { + if (!stock || !__consume_obj_stock(objcg, stock, batch_bytes)) { size_t remainder; unlock_stock(stock); - if (__obj_cgroup_charge(objcg, flags, obj_size, &remainder)) + if (__obj_cgroup_charge(objcg, flags, batch_bytes, &remainder)) return false; stock = trylock_stock(); if (remainder) __refill_obj_stock(objcg, stock, remainder, false); } - __account_obj_stock(objcg, stock, obj_size, - slab_pgdat(slab), cache_vmstat_idx(s)); + __account_obj_stock(objcg, stock, batch_bytes, + pgdat, cache_vmstat_idx(s)); unlock_stock(stock); - obj_exts = slab_obj_exts(slab); - get_slab_obj_exts(obj_exts); - off = obj_to_index(s, slab, p[i]); - obj_ext = slab_obj_ext(slab, obj_exts, off); - obj_cgroup_get(objcg); - obj_ext->objcg = objcg; - put_slab_obj_exts(obj_exts); + for (j = 0; j < run_len; j++) { + slab = virt_to_slab(p[i + j]); + obj_exts = slab_obj_exts(slab); + get_slab_obj_exts(obj_exts); + off = obj_to_index(s, slab, p[i + j]); + obj_ext = slab_obj_ext(slab, obj_exts, off); + obj_cgroup_get(objcg); + obj_ext->objcg = objcg; + put_slab_obj_exts(obj_exts); + } + + if (skip_next) + i = i + run_len + 1; + else + i += run_len; } return true; -- 2.43.0