On Thu, Apr 04, 2024 at 07:00:51PM -0400, Kent Overstreet wrote: > On Thu, Apr 04, 2024 at 03:41:50PM -0700, Andrew Morton wrote: > > On Thu, 4 Apr 2024 18:38:39 -0400 Kent Overstreet <kent.overstreet@xxxxxxxxx> wrote: > > > > > On Thu, Apr 04, 2024 at 11:33:22PM +0100, Matthew Wilcox wrote: > > > > On Thu, Apr 04, 2024 at 03:17:43PM -0700, Suren Baghdasaryan wrote: > > > > > Ironically, checkpatch generates warnings for these type casts: > > > > > > > > > > WARNING: unnecessary cast may hide bugs, see > > > > > http://c-faq.com/malloc/mallocnocast.html > > > > > #425: FILE: include/linux/dma-fence-chain.h:90: > > > > > + ((struct dma_fence_chain *)kmalloc(sizeof(struct dma_fence_chain), > > > > > GFP_KERNEL)) > > > > > > > > > > I guess I can safely ignore them in this case (since we cast to the > > > > > expected type)? > > > > > > > > I find ignoring checkpatch to be a solid move 99% of the time. > > > > > > > > I really don't like the codetags. This is so much churn, and it could > > > > all be avoided by just passing in _RET_IP_ or _THIS_IP_ depending on > > > > whether we wanted to profile this function or its caller. vmalloc > > > > has done it this way since 2008 (OK, using __builtin_return_address()) > > > > and lockdep has used _THIS_IP_ / _RET_IP_ since 2006. > > > > > > Except you can't. We've been over this; using that approach for tracing > > > is one thing, using it for actual accounting isn't workable. > > > > I missed that. There have been many emails. Please remind us of the > > reasoning here. > > I think it's on the other people claiming 'oh this would be so easy if > you just do it this other way' to put up some code - or at least more > than hot takes. Well, /proc/vmallocinfo exists, and has existed since 2008, so this is slightly more than a "hot take". > But, since you asked - one of the main goals of this patchset was to be > fast enough to run in production, and if you do it by return address > then you've added at minimum a hash table lookup to every allocate and > free; if you do that, running it in production is completely out of the > question. And yet vmalloc doesn't do that. > Besides that - the issues with annotating and tracking the correct > callsite really don't go away, they just shift around a bit. It's true > that the return address approach would be easier initially, but that's > not all we're concerned with; we're concerned with making sure > allocations get accounted to the _correct_ callsite so that we're giving > numbers that you can trust, and by making things less explicit you make > that harder. I'm not convinced that _THIS_IP_ is less precise than a codetag. They do essentially the same thing, except that codetags embed the source location in the file while _THIS_IP_ requires a tool like faddr2line to decode kernel_clone+0xc0/0x430 into a file + line number. > This is all stuff that I've explained before; let's please dial back on > the whining - or I'll just bookmark this for next time... Please stop mischaracterising serious thoughtful criticism as whining. I don't understand what value codetags bring over using _THIS_IP_ and _RET_IP_ and you need to explain that.
