linux-ext4 - Re: [PATCH 1/2] ext4: mballoc

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Date:   Sat, 30 May 2020 04:57:39 +0000
From:   Alex Zhuravlev <azhuravlev@...mcloud.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>
CC:     "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 1/2] ext4:  mballoc - prefetching for bitmaps

> On 28 May 2020, at 17:47, Theodore Y. Ts'o <tytso@....edu> wrote:
> 
> What are you trying to do here?  If nr > 0, we return; if nr < 0, we
> BUG() --- but nr is an unsigned int, so we never can trigger --- which
> was the warning reported by the kbuild test bot.  So we will only get
> past this point if ac_prefetch == group.  But ac_prefetch appears to
> be the last group that we prefetched, so it's not clear that the logic
> is correct here.

You’re right, this part “evolved” since the initial version, but I forgot to make it clear.
Basically this should be replaced with:

If (ac->ac_prefetch != group)
	return;

ac->ac_prefetch is just a cursor for the current process.

Thanks, Alex