Re: [PATCH v3 2/2] mm: tlb: add tlb swap entries batch async release

[Barry Song]

On Tue, Sep 10, 2024 at 2:44 AM zhiguojiang <justinjiang@xxxxxxxx> wrote:
>
>
>
> 在 2024/9/9 14:49, David Hildenbrand 写道:
> > On 05.08.24 17:36, Zhiguo Jiang wrote:
> >> One of the main reasons for the prolonged exit of the process with
> >> independent mm is the time-consuming release of its swap entries.
> >> The proportion of swap memory occupied by the process increases over
> >> time due to high memory pressure triggering to reclaim anonymous folio
> >> into swapspace, e.g., in Android devices, we found this proportion can
> >> reach 60% or more after a period of time. Additionally, the relatively
> >> lengthy path for releasing swap entries further contributes to the
> >> longer time required to release swap entries.
> >>
> >> Testing Platform: 8GB RAM
> >> Testing procedure:
> >> After booting up, start 15 processes first, and then observe the
> >> physical memory size occupied by the last launched process at different
> >> time points.
> >> Example: The process launched last: com.qiyi.video
> >> |  memory type  |  0min  |  1min  |   5min  |   10min  | 15min  |
> >> -------------------------------------------------------------------
> >> |     VmRSS(KB) | 453832 | 252300 |  204364 |   199944 | 199748  |
> >> |   RssAnon(KB) | 247348 |  99296 |   71268 |    67808 | 67660  |
> >> |   RssFile(KB) | 205536 | 152020 |  132144 |   131184 | 131136  |
> >> |  RssShmem(KB) |   1048 |    984 |     952 |     952  | 952  |
> >> |    VmSwap(KB) | 202692 | 334852 |  362880 |   366340 | 366488  |
> >> | Swap ratio(%) | 30.87% | 57.03% |  63.97% |   64.69% | 64.72%  |
> >> Note: min - minute.
> >>
> >> When there are multiple processes with independent mm and the high
> >> memory pressure in system, if the large memory required process is
> >> launched at this time, system will is likely to trigger the
> >> instantaneous
> >> killing of many processes with independent mm. Due to multiple exiting
> >> processes occupying multiple CPU core resources for concurrent
> >> execution,
> >> leading to some issues such as the current non-exiting and important
> >> processes lagging.
> >>
> >> To solve this problem, we have introduced the multiple exiting process
> >> asynchronous swap entries release mechanism, which isolates and caches
> >> swap entries occupied by multiple exiting processes, and hands them over
> >> to an asynchronous kworker to complete the release. This allows the
> >> exiting processes to complete quickly and release CPU resources. We have
> >> validated this modification on the Android products and achieved the
> >> expected benefits.
> >>
> >> Testing Platform: 8GB RAM
> >> Testing procedure:
> >> After restarting the machine, start 15 app processes first, and then
> >> start the camera app processes, we monitor the cold start and preview
> >> time datas of the camera app processes.
> >>
> >> Test datas of camera processes cold start time (unit: millisecond):
> >> |  seq   |   1  |   2  |   3  |   4  |   5  |   6  | average |
> >> | before | 1498 | 1476 | 1741 | 1337 | 1367 | 1655 |   1512  |
> >> | after  | 1396 | 1107 | 1136 | 1178 | 1071 | 1339 |   1204  |
> >>
> >> Test datas of camera processes preview time (unit: millisecond):
> >> |  seq   |   1  |   2  |   3  |   4  |   5  |   6  | average |
> >> | before |  267 |  402 |  504 |  513 |  161 |  265 |   352   |
> >> | after  |  188 |  223 |  301 |  203 |  162 |  154 |   205   |
> >>
> >> Base on the average of the six sets of test datas above, we can see that
> >> the benefit datas of the modified patch:
> >> 1. The cold start time of camera app processes has reduced by about 20%.
> >> 2. The preview time of camera app processes has reduced by about 42%.
> >>
> >> It offers several benefits:
> >> 1. Alleviate the high system cpu loading caused by multiple exiting
> >>     processes running simultaneously.
> >> 2. Reduce lock competition in swap entry free path by an asynchronous
> >>     kworker instead of multiple exiting processes parallel execution.
> >> 3. Release pte_present memory occupied by exiting processes more
> >>     efficiently.
> >>
> >> Signed-off-by: Zhiguo Jiang <justinjiang@xxxxxxxx>
> >> ---
> >>   arch/s390/include/asm/tlb.h |   8 +
> >>   include/asm-generic/tlb.h   |  44 ++++++
> >>   include/linux/mm_types.h    |  58 +++++++
> >>   mm/memory.c                 |   3 +-
> >>   mm/mmu_gather.c             | 296 ++++++++++++++++++++++++++++++++++++
> >>   5 files changed, 408 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/arch/s390/include/asm/tlb.h b/arch/s390/include/asm/tlb.h
> >> index e95b2c8081eb..3f681f63390f
> >> --- a/arch/s390/include/asm/tlb.h
> >> +++ b/arch/s390/include/asm/tlb.h
> >> @@ -28,6 +28,8 @@ static inline bool __tlb_remove_page_size(struct
> >> mmu_gather *tlb,
> >>           struct page *page, bool delay_rmap, int page_size);
> >>   static inline bool __tlb_remove_folio_pages(struct mmu_gather *tlb,
> >>           struct page *page, unsigned int nr_pages, bool delay_rmap);
> >> +static inline bool __tlb_remove_swap_entries(struct mmu_gather *tlb,
> >> +        swp_entry_t entry, int nr);
> >
> >
> > The problem I am having is that swap entries don't have any
> > intersection with the TLB. It sounds like we're squeezing something
> > into an existing concept (MMU gather) that just doesn't belong in there.
> I referred to the mechanism of batch release in tlb, and perhaps a new
> structure needs to be created to implement this feature.

We already use swap_slots_cache to collect multiple swap entries and
free them in
batches. Would it be better to incorporate our new logic there? might
be much less
change and don't need to touch zap_pte_range() ?  for example, while slot_caches
are almost full, wake up the async thread to free? Or, do you think
that cache->free_lock
is also a contended lock?

>
> Thanks
> Zhiguo
>

Thanks
Barry