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Date:      Tue, 07 Oct 2025 11:00:10 +0200
From:      Olivier Certner <olce@freebsd.org>
To:        Mateusz Guzik <mjguzik@gmail.com>, Mateusz Guzik <mjg@freebsd.org>
Cc:        Konstantin Belousov <kostikbel@gmail.com>, src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org
Subject:   Re: git: 84f981ba57e7 - main - nullfs: shrink null_node to 32 bytes
Message-ID:  <2940490.iL6vRArjjl@ravel>
In-Reply-To: <CAGudoHEf%2BVzj_ZTv8otuz_FCh3CfO_tok=%2BbGS=__u5qnBkuJA@mail.gmail.com>
References:  <202510061823.596IN7oZ084715@gitrepo.freebsd.org> <CAGudoHEWXDwcsXcz=NtHBWFiO48DvRBNCEQFLHXJs52TpbnJWA@mail.gmail.com> <CAGudoHEf%2BVzj_ZTv8otuz_FCh3CfO_tok=%2BbGS=__u5qnBkuJA@mail.gmail.com>

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From: Olivier Certner <olce@freebsd.org>
To: Mateusz Guzik <mjguzik@gmail.com>, Mateusz Guzik <mjg@freebsd.org>
Date: Tue, 07 Oct 2025 11:00:10 +0200
Message-ID: <2940490.iL6vRArjjl@ravel>
MIME-Version: 1.0

> > For the hash to be at all useful the chains are supposed to be short.
> >
> > Or to put it differently, a sensibly sized hash with a sensible
> > hashing function makes it automatically fine.
> >
> > This was worthwhile to do because the original size of 40 bytes is a
> > very poor fit for the allocator.
> >
> > fwiw the namecache already works this way for few years.
> >
> > the regular vnode hash should probably get the same treatment, saving
> > 8 bytes off of struct vnode
> 
> I can concede it would make sense to include this in the commit message.

That's a reasonable trade-off, but it's important that such choices are explained in the commit message and/or code comments.

Next time, please consider putting up Phabricator reviews even for such "small" changes, where we would have had the opportunity to mention this before commit.

Thanks and regards.

-- 
Olivier Certner
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