回复: [PATCH RFC] mm: mglru: provide a separate list for lazyfree anon folios

[gaoxu]

> 
> On Wed, Sep 18, 2024 at 12:02 AM David Hildenbrand <david@xxxxxxxxxx>
> wrote:
> >
> > On 14.09.24 08:37, Barry Song wrote:
> > > From: Barry Song <v-songbaohua@xxxxxxxx>
> > >
> > > This follows up on the discussion regarding Gaoxu's work[1]. It's
> > > unclear if there's still interest in implementing a separate LRU
> > > list for lazyfree folios, but I decided to explore it out of
> > > curiosity.
> > >
> > > According to Lokesh, MADV_FREE'd anon folios are expected to be
> > > released earlier than file folios. One option, as implemented by Gao
> > > Xu, is to place lazyfree anon folios at the tail of the file's
> > > `min_seq` generation. However, this approach results in lazyfree
> > > folios being released in a LIFO manner, which conflicts with LRU
> > > behavior, as noted by Michal.
> > >
> > > To address this, this patch proposes maintaining a separate list for
> > > lazyfree anon folios while keeping them classified under the "file"
> > > LRU type to minimize code changes. These lazyfree anon folios will
> > > still be counted as file folios and share the same generation with
> > > regular files. In the eviction path, the lazyfree list will be
> > > prioritized for scanning before the actual file LRU list.
> > >
> >
> > What's the downside of another LRU list? Do we have any experience on that?
> 
> Essentially, the goal is to address the downsides of using a single LRU list for files
> and lazyfree anonymous pages - seriously more files re-faults.
> 
> I'm not entirely clear on the downsides of having an additional LRU list. While it
> does increase complexity, it doesn't seem to be significant.
> 
> Let's wait for Gaoxu's test results before deciding on the next steps.
> I was just
> curious about how difficult it would be to add a separate list, so I took two hours
> to explore it :-)
Hi song,
I'm very sorry, various reasons combined have caused the delay in the results.

Basic version：android V (enable Android ART use MADV_FREE)
Test cases: 60 apps repeatedly restarted, tested for 8 hours;
The test results are as follows:
        workingset_refault_anon   workingset_refault_file
base        42016805                92010542
patch       19834873                49383572
% diff       -52.79%                  -46.33%

Additionally, a comparative test was conducted on
add-lazyfree-folio-to-lru-tail.patch[1], and the results are as follows:
               workingset_refault_anon   workingset_refault_file
lazyfree-tail        20313395                 52203061
patch             19834873                 49383572
% diff              -2.36%                    -5.40%

From the results, it can be seen that this patch is very beneficial and
better than the results in [1]; it can solve the performance issue of high
IO caused by extensive use of MADV_FREE on the Android platform.

Test case notes: There is a discrepancy between the test results mentioned in
[1] and the current test results because the test cases are different. The test
case used in [1] involves actions such as clicking and swiping within the app
after it starts; For the sake of convenience and result stability, the current
test case only involves app startup without clicking and swiping, and the number
of apps has been increased (30->60).

1. https://lore.kernel.org/all/f29f64e29c08427b95e3df30a5770056@xxxxxxxxx/T/#u
> 
> >
> > --
> > Cheers,
> >
> > David / dhildenb
> >
> 
> Thanks
> Barry