kmalloc's API family is critical for mm, and one of its nature is that it will round up the request size to a fixed one (mostly power of 2). When user requests memory for '2^n + 1' bytes, actually 2^(n+1) bytes could be allocated, so in worst case, there is around 50% memory space waste. The wastage is not a big issue for requests that get allocated/freed quickly, but may cause problems with objects that have longer life time, and there were some OOM cases in some extrem cases. This patchset tries to : * Add a debug method to track each kmalloced object's wastage info, and show the call stack of original allocation * Extend the redzone sanity check to the extra kmalloced buffer than requested, to better detect un-legitimate access to it. Please help to review, thanks! - Feng --- Changelogs: since v2: * rebased against slab tree's 'for-next' branch * fix pointer handling (Kefeng Wang) * move kzalloc zeroing handling change to a separate patch (Vlastimil Babka) * make 'orig_size' only depend on KMALLOC & STORE_USER flag bits (Vlastimil Babka) since v1: * limit the 'orig_size' to kmalloc objects only, and save it after track in metadata (Vlastimil Babka) * fix a offset calculation problem in print_trailer since RFC: * fix problems in kmem_cache_alloc_bulk() and records sorting, improve the print format (Hyeonggon Yoo) * fix a compiling issue found by 0Day bot * update the commit log based info from iova developers Feng Tang (3): mm/slub: enable debugging memory wasting of kmalloc mm/slub: only zero the requested size of buffer for kzalloc mm/slub: extend redzone check to cover extra allocated kmalloc space than requested include/linux/slab.h | 2 + mm/slab.c | 8 +-- mm/slab.h | 9 ++- mm/slub.c | 157 ++++++++++++++++++++++++++++++++++++------- 4 files changed, 146 insertions(+), 30 deletions(-) -- 2.27.0