linux-kernel - Re: [PATCH V2] mm/thp: Make ALLOC_SPLIT_PTLOCKS dependent on USE_SPLIT_PTE

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Date:   Thu, 1 Jul 2021 13:57:29 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Vlastimil Babka <vbabka@...e.cz>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] mm/thp: Make ALLOC_SPLIT_PTLOCKS dependent on
 USE_SPLIT_PTE_PTLOCKS

On Thu, Jul 01, 2021 at 10:51:27AM +0530, Anshuman Khandual wrote:
> 
> 
> On 5/20/21 4:47 PM, Matthew Wilcox wrote:
> > On Wed, May 19, 2021 at 01:03:06PM +0530, Anshuman Khandual wrote:
> >> Split ptlocks need not be defined and allocated unless they are being used.
> >> ALLOC_SPLIT_PTLOCKS is inherently dependent on USE_SPLIT_PTE_PTLOCKS. This
> >> just makes it explicit and clear. While here drop the spinlock_t element
> >> from the struct page when USE_SPLIT_PTE_PTLOCKS is not enabled.
> > 
> > I didn't spot this email yesterday.  I'm not a fan.  Isn't struct page
> > already complicated enough without adding another ifdef to it?  Surely
> > there's a better way than this.
> 
> This discussion thread just got dropped off the radar, sorry about it.
> None of the spinlock_t elements are required unless split ptlocks are
> in use. I understand your concern regarding yet another #ifdef in the
> struct page definition. But this change is simple and minimal. Do you
> have any other particular alternative in mind which I could explore ?

Do nothing?  I don't understand what problem you're trying to solve.