linux-kernel - Re: [PATCH v3 4/9] mm: introduce skip_none

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Message-ID: <77b1eddf-7c1b-43e9-9352-229998ce3fc7@redhat.com>
Date: Fri, 15 Nov 2024 11:22:31 +0100
From: David Hildenbrand <david@...hat.com>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: jannh@...gle.com, hughd@...gle.com, willy@...radead.org,
 muchun.song@...ux.dev, vbabka@...nel.org, akpm@...ux-foundation.org,
 peterx@...hat.com, mgorman@...e.de, catalin.marinas@....com,
 will@...nel.org, dave.hansen@...ux.intel.com, luto@...nel.org,
 peterz@...radead.org, x86@...nel.org, lorenzo.stoakes@...cle.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, zokeefe@...gle.com,
 rientjes@...gle.com
Subject: Re: [PATCH v3 4/9] mm: introduce skip_none_ptes()

>>> *nr_skip = nr;
>>>
>>> and then:
>>>
>>> zap_pte_range
>>> --> nr = do_zap_pte_range(tlb, vma, pte, addr, end, details, &skip_nr,
>>>                           rss, &force_flush, &force_break);
>>>        if (can_reclaim_pt) {
>>>            none_nr += count_pte_none(pte, nr);
>>>            none_nr += nr_skip;
>>>        }
>>>
>>> Right?
>>
>> Yes. I did not look closely at the patch that adds the counting of
> 
> Got it.
> 
>> pte_none though (to digest why it is required :) ).
> 
> Because 'none_nr == PTRS_PER_PTE' is used in patch #7 to detect
> empty PTE page.

Okay, so the problem is that "nr" would be "all processed entries" but 
there are cases where we "process an entry but not zap it".

What you really only want to know is "was any entry not zapped", which 
could be a simple input boolean variable passed into do_zap_pte_range?

Because as soon as any entry was processed but  no zapped, you can 
immediately give up on reclaiming that table.

> 
> Looking forward to your more review feedback on this series.

Thanks for all your hard work on this, I'm only able to make slow 
progress because I keep getting distracted by all different kinds of 
things :(

-- 
Cheers,

David / dhildenb