linux-kernel - Re: [PATCH v3 2/6] mm/huge_memory: convert "tva_flags" to "enum tva

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Message-ID: <aa1666eb-022b-4d2b-9f2a-6c8f79237c50@linux.alibaba.com>
Date: Tue, 5 Aug 2025 09:41:32 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Usama Arif <usamaarif642@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>, david@...hat.com,
 linux-mm@...ck.org
Cc: 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,
 laoar.shao@...il.com, dev.jain@....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 v3 2/6] mm/huge_memory: convert "tva_flags" to "enum
 tva_type"



On 2025/8/4 23:40, Usama Arif 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>
> ---

Looks really nice. Thanks.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>