linux-kernel - Re: [PATCH v4 24/34] mm/memcontrol.c: Convert to printbuf

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Date:   Mon, 20 Jun 2022 11:13:56 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, pmladek@...e.com,
        rostedt@...dmis.org, enozhatsky@...omium.org,
        linux@...musvillemoes.dk, willy@...radead.org
Subject: Re: [PATCH v4 24/34] mm/memcontrol.c: Convert to printbuf

On Mon, Jun 20, 2022 at 01:37:56PM +0200, Michal Hocko wrote:
> On Sun 19-06-22 20:42:23, Kent Overstreet wrote:
> > This converts memory_stat_format() from seq_buf to printbuf. Printbuf is
> > simalar to seq_buf except that it heap allocates the string buffer:
> > here, we were already heap allocating the buffer with kmalloc() so the
> > conversion is trivial.
> > 
> > Signed-off-by: Kent Overstreet <kent.overstreet@...il.com>
> 
> I have asked for a justification two times already not hearing anything.
> Please drop this patch. I do not see any actual advantage of the
> conversion. The primary downside of the existing code is that an
> internal buffer is exposed to the caller which is error prone and ugly.
> The conversion doesn't really address that part.

Do you want to tone down the hostility? Yeesh.

This patch is part of a wider series that deletes seq_buf, if you missed it here
you go: https://lore.kernel.org/all/20220620004233.3805-1-kent.overstreet@gmail.com/

> Moreover there is an inconsistency between failrure case where the
> printbuf is destroyed by a docummented way (printbuf_exit) and when the
> caller frees the buffer directly. If printbuf_exit evers need to do more
> than just kfree (e.g. kvfree) then this is a subtle bug hard to find.

Ok, _that's_ a technical point we can talk about and address. I'll add
documentation to the printbuf code that the buffer must be freeable with
kfree().