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

[Song Liu]

Hi Hillf,

> On Jun 23, 2019, at 8:16 PM, Hillf Danton <hdanton@xxxxxxxx> 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@xxxxxxxxxxx>
>> Signed-off-by: Song Liu <songliubraving@xxxxxx>
>> ---
>> 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