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

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Message-ID: <E2CC7BF8-A3F2-4F14-BBDE-94B635FA1795@nvidia.com>
Date: Thu, 14 Aug 2025 10:59:18 -0400
From: Zi Yan <ziy@...dia.com>
To: Usama Arif <usamaarif642@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, david@...hat.com,
 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,
 laoar.shao@...il.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 13 Aug 2025, at 9:55, 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>
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
>  fs/proc/task_mmu.c      |  4 ++--
>  include/linux/huge_mm.h | 30 ++++++++++++++++++------------
>  mm/huge_memory.c        |  8 ++++----
>  mm/khugepaged.c         | 17 ++++++++---------
>  mm/memory.c             | 14 ++++++--------
>  5 files changed, 38 insertions(+), 35 deletions(-)
>

Reviewed-by: Zi Yan <ziy@...dia.com>

Best Regards,
Yan, Zi