From: Christopher Lameter <cl@xxxxxxxxx> Date: 2020-04-17 23:59:00 To: Bernard Zhao <bernard@xxxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx>,David Rientjes <rientjes@xxxxxxxxxx>,Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>,Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>,linux-mm@xxxxxxxxx,linux-kernel@xxxxxxxxxxxxxxx,kernel@xxxxxxxx Subject: Re: [PATCH] kmalloc_index optimization(add kmalloc max size check)>On Fri, 17 Apr 2020, Bernard Zhao wrote: > >> kmalloc size should never exceed KMALLOC_MAX_SIZE. >> kmalloc_index realise if size is exceed KMALLOC_MAX_SIZE, e.g 64M, >> kmalloc_index just return index 26, but never check with OS`s max >> kmalloc config KMALLOC_MAX_SIZE. This index`s kmalloc caches maybe >> not create in function create_kmalloc_caches. >> We can throw an warninginfo in kmalloc at the beginning, instead of >> being guaranteed by the buddy alloc behind. > >kmalloc_index(0 already bugs if the allocation is more than 64M > > >... > > if (size <= 64 * 1024 * 1024) return 26; > BUG(); > > >You could modify that to check for KMALLOC_MAX_SIZE with some more >conditionals but then kmalloc_index) is written so that the compiler gets >constant folding right. > >If you have a patch like that then please verify that all c compilers in >use perform correct constant folding and do not add unnecessary code. > > Sorry for the misunderstanding. What I meant was that the “if”in kmalloc_index should be consistent with KMALLOC_MAX_SIZE. For example, if the MAX_ZONEORDER configured by the kernel is 11, which is 4M, then size >4M should trigger BUG(). If the configuration is smaller, e.g MAX_ZONEORDER is 9, 1M, then the size > 1M should be BUG. But the current code is not, kmalloc_index will only be BUG() when it exceeds 64M.
