Hi Michal,
>> 5) To check number of entries in stackdepot to decide stackdepot hash size >> for different systems. >> For fewer entries hash table size can be reduced from 4MB. > > What are you going to do with that information. It is not like you can > reduce the memory footprint or somehow optimize anything during the > runtime. On low memory system where page owner entries are in range of 3k ~ 4k, its a waste to keep hash table size of 4MB. It can be modified to some 128KB to save memory footprint of stackdepot. So stackdepot entry count is important. > OK, so debugging a debugging facility... I do not think we want to > introduce a lot of code for something like that. We enabled stackdepot on our system and realised, in long run stack depot consumes more runtime memory then it actually needs. we used shared patch to debug this issue. stack stores following two unique entries. Page allocation done in interrupt context will generate a unique stack trace. Consider following two entries. Entry 1: __alloc_pages_nodemask+0xec/0x200 page_frag_alloc+0x84/0x140 __napi_alloc_skb+0x83/0xe0 rtl8169_poll+0x1e5/0x670 net_rx_action+0x122/0x380 __do_softirq+0xce/0x298 irq_exit+0xa3/0xb0 ------------------- do_IRQ+0x72/0xc0 ret_from_intr+0x0/0x14 rw_copy_check_uvector+0x8a/0x100 import_iovec+0x27/0xc0 copy_msghdr_from_user+0xc0/0x120 ___sys_recvmsg+0x76/0x210 __sys_recvmsg+0x39/0x70 entry_SYSCALL_64_fastpath+0x13/ Entry 2: __alloc_pages_nodemask+0xec/0x200 page_frag_alloc+0x84/0x140 __napi_alloc_skb+0x83/0xe0 rtl8169_poll+0x1e5/0x670 net_rx_action+0x122/0x380 __do_softirq+0xce/0x298 irq_exit+0xa3/0xb0 ------------------- smp_apic_timer_interrupt+0x5b/0x110 apic_timer_interrupt+0x89/0x90 cpuidle_enter_state+0x95/0x2c0 do_idle+0x163/0x1a0 cpu_startup_entry+0x14/0x20 secondary_startup_64+0xa5/0xb0 Actual Allocation Path is __alloc_pages_nodemask+0xec/0x200 page_frag_alloc+0x84/0x140 __napi_alloc_skb+0x83/0xe0 rtl8169_poll+0x1e5/0x670 net_rx_action+0x122/0x380 __do_softirq+0xce/0x298 irq_exit+0xa3/0xb0 We have been getting similar kind of such entries and eventually stackdepot reaches Max Cap. So we found this interface useful in debugging stackdepot issue so shared in community. Regards, Vaneet Narang
