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

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Message-ID: <jb25mtkveqf63bv74jhynf6ncxmums5s37esveqsv52yurh4z7@5q55ttv34bia>
Date: Thu, 4 Apr 2024 18:38:39 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Matthew Wilcox <willy@...radead.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org, 
	joro@...tes.org, will@...nel.org, trond.myklebust@...merspace.com, 
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	jikos@...nel.org, benjamin.tissoires@...hat.com, tytso@....edu, jack@...e.com, 
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	linux-mm@...ck.org, netdev@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH 1/1] mm: change inlined allocation helpers to account at
 the call site

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.