linux-kernel - Re: [PATCH v4 2/7] mm/huge_memory: convert "tva_flags" to "enum tva

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Message-ID: <c8a47a7d-3810-426f-a2cf-7c020ce25c7d@gmail.com>
Date: Thu, 14 Aug 2025 11:43:16 +0100
From: Usama Arif <usamaarif642@...il.com>
To: Yafang Shao <laoar.shao@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>, david@...hat.com
Cc: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, corbet@....net,
 rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, hannes@...xchg.org,
 baohua@...nel.org, shakeel.butt@...ux.dev, riel@...riel.com, ziy@...dia.com,
 dev.jain@....com, baolin.wang@...ux.alibaba.com, npache@...hat.com,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, ryan.roberts@....com,
 vbabka@...e.cz, jannh@...gle.com, Arnd Bergmann <arnd@...db.de>,
 sj@...nel.org, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 kernel-team@...a.com
Subject: Re: [PATCH v4 2/7] mm/huge_memory: convert "tva_flags" to "enum
 tva_type"



On 14/08/2025 04:07, Yafang Shao wrote:
> On Wed, Aug 13, 2025 at 9:57 PM Usama Arif <usamaarif642@...il.com> wrote:
>>
>> From: David Hildenbrand <david@...hat.com>
>>
>> When determining which THP orders are eligible for a VMA mapping,
>> we have previously specified tva_flags, however it turns out it is
>> really not necessary to treat these as flags.
>>
>> Rather, we distinguish between distinct modes.
>>
>> The only case where we previously combined flags was with
>> TVA_ENFORCE_SYSFS, but we can avoid this by observing that this
>> is the default, except for MADV_COLLAPSE or an edge cases in
>> collapse_pte_mapped_thp() and hugepage_vma_revalidate(), and
>> adding a mode specifically for this case - TVA_FORCED_COLLAPSE.
>>
>> We have:
>> * smaps handling for showing "THPeligible"
>> * Pagefault handling
>> * khugepaged handling
>> * Forced collapse handling: primarily MADV_COLLAPSE, but also for
>>   an edge case in collapse_pte_mapped_thp()
>>
>> Disregarding the edge cases, we only want to ignore sysfs settings only
>> when we are forcing a collapse through MADV_COLLAPSE, otherwise we
>> want to enforce it, hence this patch does the following flag to enum
>> conversions:
>>
>> * TVA_SMAPS | TVA_ENFORCE_SYSFS -> TVA_SMAPS
>> * TVA_IN_PF | TVA_ENFORCE_SYSFS -> TVA_PAGEFAULT
>> * TVA_ENFORCE_SYSFS             -> TVA_KHUGEPAGED
>> * 0                             -> TVA_FORCED_COLLAPSE
>>
>> With this change, we immediately know if we are in the forced collapse
>> case, which will be valuable next.
>>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> Acked-by: Usama Arif <usamaarif642@...il.com>
>> Signed-off-by: Usama Arif <usamaarif642@...il.com>
>> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> 
> Acked-by: Yafang Shao <laoar.shao@...il.com>
> 
> Hello Usama,
> 
> This change is also required by my BPF-based THP order selection
> series [0]. Since this patch appears to be independent of the series,
> could we merge it first into mm-new or mm-everything if the series
> itself won't be merged shortly?
> 
> Link: https://lwn.net/Articles/1031829/ [0]
> 

Thanks for reviewing!

All of the patches in the series have several acks/reviews. Only a small change
might be required in selftest, so hopefully the next revision is the last one.

Andrew - would it be ok to start including this entire series in the mm-new now?

Thanks!