linux-kernel - Re: [PATCH v10 6/7] mm,thp: add read-only THP support for (non-shmem) FS

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Date:   Mon, 12 Aug 2019 16:36:14 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Song Liu <songliubraving@...com>
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, matthew.wilcox@...cle.com,
        kirill.shutemov@...ux.intel.com, kernel-team@...com,
        william.kucharski@...cle.com, akpm@...ux-foundation.org,
        hdanton@...a.com
Subject: Re: [PATCH v10 6/7] mm,thp: add read-only THP support for
 (non-shmem) FS

On Thu, Aug 01, 2019 at 11:42:43AM -0700, Song Liu wrote:
> This patch is (hopefully) the first step to enable THP for non-shmem
> filesystems.
> 
> This patch enables an application to put part of its text sections to THP
> via madvise, for example:
> 
>     madvise((void *)0x600000, 0x200000, MADV_HUGEPAGE);
> 
> We tried to reuse the logic for THP on tmpfs.
> 
> Currently, write is not supported for non-shmem THP. khugepaged will only
> process vma with VM_DENYWRITE. sys_mmap() ignores VM_DENYWRITE requests
> (see ksys_mmap_pgoff). The only way to create vma with VM_DENYWRITE is
> execve(). This requirement limits non-shmem THP to text sections.
> 
> The next patch will handle writes, which would only happen when the all
> the vmas with VM_DENYWRITE are unmapped.
> 
> An EXPERIMENTAL config, READ_ONLY_THP_FOR_FS, is added to gate this
> feature.
> 
> Cc: Johannes Weiner <hannes@...xchg.org>
> Acked-by: Rik van Riel <riel@...riel.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Signed-off-by: Song Liu <songliubraving@...com>

Acked-by: Johannes Weiner <hannes@...xchg.org>