* Yin, Fengwei <fengwei.yin@xxxxxxxxx> [230605 23:11]: > > > On 6/6/2023 11:08 AM, Hugh Dickins wrote: > > On Tue, 6 Jun 2023, Yin, Fengwei wrote: > >> On 6/6/2023 10:41 AM, Hugh Dickins wrote: > >>> On Mon, 5 Jun 2023, Liam R. Howlett wrote: > >>>> > >>>> You mean "mm: update validate_mm() to use vma iterator" here I guess. I > >>>> have it as a different commit id in my branch. > >>>> > >>>> I 'restored' some of the checking because I was able to work around not > >>>> having the mt_dump() definition with the vma iterator. I'm now > >>>> wondering how wide spread CONFIG_DEBUG_VM is used and if I should not > >>>> have added these extra checks. > >>> > >>> Most CONFIG_DEBUG_VM checks are quite cheap, mostly VM_BUG_ONs for > >> Indeed. I had CONFIG_DEBUG_VM enabled and didn't see surprise perf report. > >> > >> > >>> easily checked conditions. If validate_mm() is still the kind of thing > >>> it used to be, checking through every vma on every mmap operation, please > >>> don't bring that into CONFIG_DEBUG_VM - it distorts performance too much, > >>> so always used to be under a separate CONFIG_DEBUG_VM_RB instead. Okay, I will update my patch to use CONFIG_DEBUG_VM_MAPLE_TREE for validate_mm(). > >> So does this mean CONFIG_DEBUG_VM is allowed to be enabled for performance > >> testing? Thanks. > > > > I was going to say: > > No, I did not mean that: I just meant that even developers not doing > > strict performance testing still like to keep a rough eye on performance > > changes; and historically CONFIG_DEBUG_VM has not distorted very much. > > > > But then I wonder about certain distros which (wrongly or rightly) turn > > CONFIG_DEBUG_VM on: I expect they do performance testing on their kernels. > Fair enough. Thanks for explanation. > Thanks for looking at this everyone. Regards, Liam
