linux-kernel - Re: [PATCH] mm/huge_memory: move writeback and truncation checks early

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Message-ID: <ZjK8zDzIjN3xPR9n@bombadil.infradead.org>
Date: Wed, 1 May 2024 15:06:04 -0700
From: Luis Chamberlain <mcgrof@...nel.org>
To: David Hildenbrand <david@...hat.com>
Cc: akpm@...ux-foundation.org, ziy@...dia.com, linux-mm@...ck.org,
	fstests@...r.kernel.org, linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, willy@...radead.org, hare@...e.de,
	john.g.garry@...cle.com, p.raghav@...sung.com, da.gomez@...sung.com
Subject: Re: [PATCH] mm/huge_memory: move writeback and truncation checks
 early

On Thu, Apr 25, 2024 at 11:40:48AM +0200, David Hildenbrand wrote:
> On 25.04.24 00:57, Luis Chamberlain wrote:
> > We should check as early as possible if we should bail due to writeback
> > or truncation. This will allow us to add further sanity checks earlier
> > as well.
> > 
> > This introduces no functional changes.
> > 
> > Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> > ---
> >   mm/huge_memory.c | 23 +++++++++++------------
> >   1 file changed, 11 insertions(+), 12 deletions(-)
> > 
> > While working on min order support for LBS this came up as an improvement
> > as we can check for the min order early earlier, so this sets the stage
> > up for that.
> > 
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 86a8c7b3b8dc..32c701821e0d 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -3055,8 +3055,17 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
> >   	if (new_order >= folio_order(folio))
> >   		return -EINVAL;
> > -	/* Cannot split anonymous THP to order-1 */
> > -	if (new_order == 1 && folio_test_anon(folio)) {
> > +	if (folio_test_writeback(folio))
> > +		return -EBUSY;
> > +
> 
> Why earlier than basic input parameter checks (new_order?
> 
> Sorry, but I don't see the reason for that change. It's all happening
> extremely early, what are we concerned about?
> 
> It's likely better to send that patch with the actual patch "to add further
> sanity checks earlier as well", and why they have to be that early.

It's a clear eye-sore when we add min order, I'll leave the eyesores for
others. It can wait.

  Luis