On 27.06.23 22:13, Hugh Dickins wrote:

On Tue, 27 Jun 2023, David Hildenbrand wrote:

quoted

On 27.06.23 06:44, Hugh Dickins wrote:

quoted

On Mon, 26 Jun 2023, Vishal Moola (Oracle) wrote:

quoted

The MM subsystem is trying to shrink struct page. This patchset
introduces a memory descriptor for page table tracking - struct ptdesc.

...

quoted

   39 files changed, 686 insertions(+), 455 deletions(-)

I don't see the point of this patchset: to me it is just obfuscation of
the present-day tight relationship between page table and struct page.

Matthew already explained:

quoted

The intent is to get ptdescs to be dynamically allocated at some point
in the ~2-3 years out future when we have finished the folio project ...

So in a kindly mood, I'd say that this patchset is ahead of its time.
But I can certainly adapt to it, if everyone else sees some point to it.

I share your thoughts, that code churn which will help eventually in the far,
far future (not wanting to sound too pessimistic, but it's not going to be
there tomorrow ;) ).

However, if it's just the same as the other conversions we already did (e.g.,
struct slab), then I guess there is no reason to stop now -- the obfuscation
already happened.

... or is there a difference regarding this conversion and the previous ones?

I was aware of the struct slab thing, didn't see much point there myself
either; but it was welcomed by Vlastimil, and barely affected outside of
slab allocators, so I had no reason to object.

You think that if a little unnecessary churn (a *lot* of churn if you
include folios, which did save some repeated calls to compound_head())
has already occurred, that's a good precedent for allowing more and more?

Well, if you phrase it like that ... no, I'm not in favor of unnecessary 
churn at all. Yes, folios were/are a lot of churn (IMHO not unnecessary, 
though).

I'm not a friend of these "overlays"; it all only really makes sense to 
me once we actually allocate the descriptors dynamically. Maybe some of 
the existing/ongoing conversions were different (that's why I was asking 
for the difference, as you said the "struct slab" thing was well received).

If they are primarily only unnecessary churn for now (and unclear 
when/how it will become useful), I share your opinion.

-- 
Cheers,

David / dhildenb


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