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SubjectRe: [PATCH v7 5/6] mm,thp: add read-only THP support for (non-shmem) FS
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Hi Hillf,

> On Jun 23, 2019, at 8:16 PM, Hillf Danton <hdanton@sina.com> wrote:
>
>
> Hello
>
> On Sun, 23 Jun 2019 13:48:47 +0800 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. The next patch will handle writes, which
>> would only happen when the vma with VM_DENYWRITE is unmapped.
>>
>> An EXPERIMENTAL config, READ_ONLY_THP_FOR_FS, is added to gate this
>> feature.
>>
>> Acked-by: Rik van Riel <riel@surriel.com>
>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> ---
>> mm/Kconfig | 11 ++++++
>> mm/filemap.c | 4 +--
>> mm/khugepaged.c | 90 ++++++++++++++++++++++++++++++++++++++++---------
>> mm/rmap.c | 12 ++++---
>> 4 files changed, 96 insertions(+), 21 deletions(-)
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index f0c76ba47695..0a8fd589406d 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -762,6 +762,17 @@ config GUP_BENCHMARK
>>
>> See tools/testing/selftests/vm/gup_benchmark.c
>>
>> +config READ_ONLY_THP_FOR_FS
>> + bool "Read-only THP for filesystems (EXPERIMENTAL)"
>> + depends on TRANSPARENT_HUGE_PAGECACHE && SHMEM
>> +
> The ext4 mentioned in the cover letter, along with the subject line of
> this patch, suggests the scissoring of SHMEM.

We reuse khugepaged code for SHMEM, so the dependency does exist.

Thanks,
Song

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