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

[David Hildenbrand <david@redhat.com>]

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@vivo.com>
> ---
>   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.

-- 
Cheers,

David / dhildenb