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. 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. 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. Additionally: the alloc_hooks() macro is for more than this. It's also for more usable fault injection - remember every thread we have where people are begging for every allocation to be __GFP_NOFAIL - "oh, error paths are hard to test, let's just get rid of them" - never mind that actually do have to have error paths - but _per callsite_ selectable fault injection will actually make it practical to test memory error paths. And Kees working on stuff that'll make use of the alloc_hooks() macro for segregating kmem_caches. 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...
