linux-kernel - Re: [PATCH 4/5] mm: make vmg->target consistent and further simplify commit

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Message-ID: <afc179ed-0d85-4b73-852a-3f6ff24b82cc@lucifer.local>
Date: Wed, 29 Jan 2025 15:30:00 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Jann Horn <jannh@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] mm: make vmg->target consistent and further simplify
 commit_merge()

On Wed, Jan 29, 2025 at 04:19:50PM +0100, Vlastimil Babka wrote:
> On 1/27/25 16:50, Lorenzo Stoakes wrote:
> > + if (flags & __VMG_FLAG_REMOVE_MIDDLE) {
> > + *remove = vmg->middle;
> > + remove = &vp->remove2;
> > + }
> > + if (flags & __VMG_FLAG_REMOVE_NEXT)
> > + *remove = vmg->next;
> > +
> > + if (flags & __VMG_FLAG_ADJUST_MIDDLE_START)
> > + adjust = vmg->middle;
> > + else if (flags & __VMG_FLAG_ADJUST_NEXT_START)
> > + adjust = vmg->next;
> > + else
> > + adjust = NULL;
> > +
> > + vp->adj_next = adjust;
>
> Realized this has kinda made it more obvious that vp->adj_next is a misnomer?

Well yes and no.

It is badly named, as it sounds like adj_start, which is an offset, but it is
equivalent to 'adjust' elsewhere.

But it _is_ the 'next' VMA from the one which we are otherwise manipulating, so
'adjusted next' is sort of a vaguely reasonable-ish name.

But at the same time, it's all horrible and maybe this whole
vma_prepare()/complete() will be the target of my next round of
churn^D^D^D^D^Drefactorings...

I also don't like the various 'special casing' of these situations in
vma_complete(), and it feels like - maybe we can use or adapt the vmg structure
for split as well and put the vma_prepare()/vma_complete() stuff there too...

Anyway. One thing at a time.