linux-kernel - Re: [PATCH] xfs: add tunable threshold parameter for triggering zone GC

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Message-ID: <20250422054851.GA29297@lst.de>
Date: Tue, 22 Apr 2025 07:48:51 +0200
From: hch <hch@....de>
To: Guenter Roeck <linux@...ck-us.net>
Cc: hch <hch@....de>, Carlos Maiolino <cem@...nel.org>,
	Hans Holmberg <Hans.Holmberg@....com>,
	Dave Chinner <david@...morbit.com>,
	"Darrick J . Wong" <djwong@...nel.org>,
	"linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xfs: add tunable threshold parameter for triggering
 zone GC

On Mon, Apr 21, 2025 at 06:41:43AM -0700, Guenter Roeck wrote:
> On 4/21/25 01:31, hch wrote:
>> On Sun, Apr 20, 2025 at 10:42:56AM -0700, Guenter Roeck wrote:
>>> A possible local solution is below. Note the variable type change from s64 to u64.
>>
>> I think that'll need a lower bound of 0 thrown in to be safe as these
>> counters can occasionally underflow.
>>
>> Otherwise this is probably the right thing to do for now until mult_frac
>> gets fixed eventually.  Can you add a comment why this open codes
>> mult_frac to the code and send a formal patch for it?
>>
>
> Technically only free needs to be u64 for do_div to work. But that makes
> me wonder what the function is supposed to return if free < 0.

free should be floored to zero, i.e.

	free = min(0, xfs_estimate_freecounter(mp, XC_FREE_RTEXTENTS));