On 10/15/22 01:48, Hyeonggon Yoo wrote: > On Fri, Oct 14, 2022 at 01:58:18PM -0700, Guenter Roeck wrote: >> Hi, >> >> On Wed, Aug 17, 2022 at 07:18:19PM +0900, Hyeonggon Yoo wrote: >> > There is not much benefit for serving large objects in kmalloc(). >> > Let's pass large requests to page allocator like SLUB for better >> > maintenance of common code. >> > >> > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> >> > Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx> >> > --- >> >> This patch results in a WARNING backtrace in all mips and sparc64 >> emulations. >> >> ------------[ cut here ]------------ >> WARNING: CPU: 0 PID: 0 at mm/slab_common.c:729 kmalloc_slab+0xc0/0xdc >> Modules linked in: >> CPU: 0 PID: 0 Comm: swapper Not tainted 6.0.0-11990-g9c9155a3509a #1 >> Stack : ffffffff 801b2a18 80dd0000 00000004 00000000 00000000 81023cd4 00000000 >> 81040000 811a9930 81040000 8104a628 81101833 00000001 81023c78 00000000 >> 00000000 00000000 80f5d858 81023b98 00000001 00000023 00000000 ffffffff >> 00000000 00000064 00000002 81040000 81040000 00000001 80f5d858 000002d9 >> 00000000 00000000 80000000 80002000 00000000 00000000 00000000 00000000 >> ... >> Call Trace: >> [<8010a2bc>] show_stack+0x38/0x118 >> [<80cf5f7c>] dump_stack_lvl+0xac/0x104 >> [<80130d7c>] __warn+0xe0/0x224 >> [<80cdba5c>] warn_slowpath_fmt+0x64/0xb8 >> [<8028c058>] kmalloc_slab+0xc0/0xdc >> >> irq event stamp: 0 >> hardirqs last enabled at (0): [<00000000>] 0x0 >> hardirqs last disabled at (0): [<00000000>] 0x0 >> softirqs last enabled at (0): [<00000000>] 0x0 >> softirqs last disabled at (0): [<00000000>] 0x0 >> ---[ end trace 0000000000000000 ]--- >> >> Guenter > > Hi. > > Thank you so much for this report! > > Hmm so SLAB tries to find kmalloc cache for freelist index array using > kmalloc_slab() directly, and it becomes problematic when size of the > array is larger than PAGE_SIZE * 2. Hmm interesting, did you find out how exactly that can happen in practice, or what's special about mips and sparc64 here? Because normally calculate_slab_order() will only go up to slab_max_order, which AFAICS can only go up to SLAB_MAX_ORDER_HI, thus 1, unless there's a boot command line override. And if we have two pages for objects, surely even with small objects they can't be smaller than freelist_idx_t, so if the number of objects fits into two pages (order 1), then the freelist array should also fit in two pages? Thanks, Vlastimil > Will send a fix soon. >
