Address review comments

Move some stuff to mem_map_base.h so that it will make the use of platform MemMap easier.

Continue how we measure the efficiency of early-exit releaseToOS in D146312,

Add some number from system_server

The evaluation is from the same scenario as above - reboot the phone and wait for 30s, then collect all the events of calling releaseToOS.

Slightly adjust the heuristic.
The new threshold should also consider PushedBytesDelta because we don't reset it after a failed page release

Maybe we can say more about the difference between M_PURGE and M_PURGE_ALL? From the description, I'm not sure that I understand which one I should use.

In D146312#4203317, @cferris wrote:

Small comment nits.

You gathered data for the one process, but is there any other data worth gathering?

I did see some extra work going on in system_server, but I was using my test account so it might have a different set of apps that triggers a different allocation pattern. Let me know if you want me to gather anything on this device.

Address review comment and fix a bug in keep the invariant that the TryReleaseThreshold.
It should be the minimum distance to the next page release. So if it has reached the high
density, then the next threshold will be the SmallerBlockReleasePageDelta (which we use for
mitigating thrashing)

In D146324#4203093, @pcc wrote:

How do you usually build Scudo? When I run the unit tests I cross compile it for Android using llvm's gn build system. If you're building it as part of the Android platform, SCUDO_PREFIX will be defined to add a prefix of scudo_, so the alias in malloc.h wouldn't affect the definitions.

Add releaseAndZeroPagesToOS and add more DCHECK in the base classes

Just curious, why we didn't have issue before? I thought it may be fine because it's defined as WEAK ?!

With this CL, the filtered try-marking-blocks is reduced ~1000 times (6000 vs 5000) in com.google.android.googlequicksearchbox:interactor on Android

Add ScopedTimer::ignore() to skip some scoped events

LGTM

1. Rename MapReserver to ReservedMap.
2. Add more comments on why ReservedMap still derives from MemMapBase
3. Leave the unused functions in ReservedMap unimplemented (which were having default implementations which does nothing)

LGTM!

Remove the defining of MapReserver in the tests

Add unamp() and remove the use of MapPlatformData in primary64

Make getCapacity as required and add few more comments

Don't define MapReserver in allocator config

So far I call it RFC but it's a formal CL as well. There are still many places we can simplify. In order to make the review process easier, I'll do the simplification in coming CLs.

No conflict at all!

default init SmallerBlockReleasePageDelta as 0 because all other fields in
primary allocator are initialized as 0. Make them consistent so that we don't
need additional static initializer. Eventually, we will override it later.

In D145419#4176234, @cferris wrote:

Are there tests that already cover the modified code?

Add more comment

Add more comments

Remove extra space and rebase

In D144768#4167951, @cferris wrote:

LGTM.

I had one small comment about a comment that is so small that I don't think it's worth holding up the CL.

Address review comment

The size is determined by collecting the buffer usage from several apps and we didn't see them over 256, most of them are smaller than 100. With partial range releasing, the required buffer size is even smaller. The following is a sample with buffer size grater than 200. It's 15 out of 312 buffer usages.

Address review comment and slightly reorganize conditional branch

Rebase only

Fix a bug on Fuchsia, ReleaseRecorder should record the offset instead of adding the offset to the base directly.

In D144920#4165510, @MaskRay wrote:

We don't upload a new patch for a reland. You can click "Add Action" -> "Reopen Revision" and reuse the original differential. This helps discussions in a centralized place.

In D142659#4165452, @MaskRay wrote:

I usually use Revert Dxxxx $original_subject instead of Revert Dxxxx $original_subject so that the revert commit is associated with this page. You can see the commit in "Commits" in the "Details" section.