linux-ext4 - Re: [PATCH 1/1] mm: change inlined allocation helpers to account at the call site

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Date: Thu, 4 Apr 2024 15:41:50 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Matthew Wilcox <willy@...radead.org>, Suren Baghdasaryan
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Subject: Re: [PATCH 1/1] mm: change inlined allocation helpers to account at
 the call site

On Thu, 4 Apr 2024 18:38:39 -0400 Kent Overstreet <kent.overstreet@...ux.dev> 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.