mm/madvise: add MADV_WILLNEED to process_madvise()

Commit Message

张魁(Kyler) Aug. 4, 2021, 8:20 a.m. UTC

There is a usecase in Android that an app process's memory is swapped out
by process_madvise() with MADV_PAGEOUT, such as the memory is swapped to
zram or a backing device. When the process is scheduled to running, like
switch to foreground, multiple page faults may cause the app dropped
frames.
To reduce the problem, SMS can read-ahead memory of the process immediately
when the app switches to forground.
Calling process_madvise() with MADV_WILLNEED can meet this need.

Signed-off-by: zhangkui <[e-mail]>
---
 mm/madvise.c | 1 +
 1 file changed, 1 insertion(+)

--
2.25.1

Comments

David Hildenbrand Aug. 4, 2021, 7:08 p.m. UTC | #1

On 04.08.21 10:20, zhangkui wrote:
> There is a usecase in Android that an app process's memory is swapped out
> by process_madvise() with MADV_PAGEOUT, such as the memory is swapped to
> zram or a backing device. When the process is scheduled to running, like
> switch to foreground, multiple page faults may cause the app dropped
> frames.
> To reduce the problem, SMS can read-ahead memory of the process immediately
> when the app switches to forground.
> Calling process_madvise() with MADV_WILLNEED can meet this need.
> 
> Signed-off-by: zhangkui <[e-mail]>
> ---
>   mm/madvise.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 6d3d348b17f4..b9681fb3fbb5 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1046,6 +1046,7 @@ process_madvise_behavior_valid(int behavior)
>          switch (behavior) {
>          case MADV_COLD:
>          case MADV_PAGEOUT:
> +       case MADV_WILLNEED:
>                  return true;
>          default:
>                  return false;

I guess this should be fine. In contrast to other (e.g., destructive) 
madvise calls, an application could merely notice the difference that 
for example, in the pagemap something is suddenly no longer swapped, 
even thought the page wasn't touched by the process. But that can also 
happen e.g., during swapoff.

So I think this is fine, but let's hear if there are concerns.

Andrew Morton Aug. 5, 2021, 2 a.m. UTC | #2

On Wed,  4 Aug 2021 16:20:10 +0800 zhangkui <[e-mail]> wrote:

> There is a usecase in Android that an app process's memory is swapped out
> by process_madvise() with MADV_PAGEOUT, such as the memory is swapped to
> zram or a backing device. When the process is scheduled to running, like
> switch to foreground, multiple page faults may cause the app dropped
> frames.
> To reduce the problem, SMS can read-ahead memory of the process immediately
> when the app switches to forground.
> Calling process_madvise() with MADV_WILLNEED can meet this need.
> 

What is SMS?

Andrew Morton Aug. 5, 2021, 2:04 a.m. UTC | #3

On Wed,  4 Aug 2021 16:20:10 +0800 zhangkui <[e-mail]> wrote:

> There is a usecase in Android that an app process's memory is swapped out
> by process_madvise() with MADV_PAGEOUT, such as the memory is swapped to
> zram or a backing device. When the process is scheduled to running, like
> switch to foreground, multiple page faults may cause the app dropped
> frames.
> To reduce the problem, SMS can read-ahead memory of the process immediately
> when the app switches to forground.
> Calling process_madvise() with MADV_WILLNEED can meet this need.

This will require a small update to the process_madvise(2) manpage. 
Can you please send a patch?

张魁(Kyler) Aug. 5, 2021, 2:58 a.m. UTC | #4

在 8/5/2021 10:00, Andrew Morton 写道:
> On Wed,  4 Aug 2021 16:20:10 +0800 zhangkui <[e-mail]> wrote:
>
>> There is a usecase in Android that an app process's memory is swapped out
>> by process_madvise() with MADV_PAGEOUT, such as the memory is swapped to
>> zram or a backing device. When the process is scheduled to running, like
>> switch to foreground, multiple page faults may cause the app dropped
>> frames.
>> To reduce the problem, SMS can read-ahead memory of the process immediately
>> when the app switches to forground.
>> Calling process_madvise() with MADV_WILLNEED can meet this need.
>>
>
> What is SMS?
>
SMS is the abbreviation of System Management Software.
For more information, please refer to the commit
ecb8ac8b1f146915aa6b96449b66dd48984caacc.

张魁(Kyler) Aug. 5, 2021, 4:50 a.m. UTC | #5

On 8/5/2021 10:04, Andrew Morton wrote:
> On Wed,  4 Aug 2021 16:20:10 +0800 zhangkui <[e-mail]> wrote:
>
>> There is a usecase in Android that an app process's memory is swapped out
>> by process_madvise() with MADV_PAGEOUT, such as the memory is swapped to
>> zram or a backing device. When the process is scheduled to running, like
>> switch to foreground, multiple page faults may cause the app dropped
>> frames.
>> To reduce the problem, SMS can read-ahead memory of the process immediately
>> when the app switches to forground.
>> Calling process_madvise() with MADV_WILLNEED can meet this need.
>
> This will require a small update to the process_madvise(2) manpage.
> Can you please send a patch?
>

I pushed a patch, please help to review it.
https://lore.kernel.org/patchwork/patch/1472380/

Patch

diff --git a/mm/madvise.c b/mm/madvise.c
index 6d3d348b17f4..b9681fb3fbb5 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1046,6 +1046,7 @@  process_madvise_behavior_valid(int behavior)
        switch (behavior) {
        case MADV_COLD:
        case MADV_PAGEOUT:
+       case MADV_WILLNEED:
                return true;
        default:
                return false;