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

From: Barry Song
Date: Tue Sep 10 2024 - 00:21:21 EST

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On Tue, Sep 10, 2024 at 2:39 AM zhiguojiang <justinjiang@xxxxxxxx> wrote:
>
>
>
> 在 2024/9/9 9:59, Barry Song 写道:
> > On Wed, Sep 4, 2024 at 11:26 PM zhiguojiang <justinjiang@xxxxxxxx> wrote:
> >>
> >>
> >> 在 2024/9/4 17:16, Barry Song 写道:
> >>> On Tue, Aug 6, 2024 at 3:36 AM Zhiguo Jiang <justinjiang@xxxxxxxx> 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);
> >>>>
> >>>> #define tlb_flush tlb_flush
> >>>> #define pte_free_tlb pte_free_tlb
> >>>> @@ -69,6 +71,12 @@ static inline bool __tlb_remove_folio_pages(struct mmu_gather *tlb,
> >>>> return false;
> >>>> }
> >>>>
> >>>> +static inline bool __tlb_remove_swap_entries(struct mmu_gather *tlb,
> >>>> + swp_entry_t entry, int nr)
> >>>> +{
> >>>> + return false;
> >>>> +}
> >>>> +
> >>>> static inline void tlb_flush(struct mmu_gather *tlb)
> >>>> {
> >>>> __tlb_flush_mm_lazy(tlb->mm);
> >>>> diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
> >>>> index 709830274b75..8b4d516b35b8
> >>>> --- a/include/asm-generic/tlb.h
> >>>> +++ b/include/asm-generic/tlb.h
> >>>> @@ -294,6 +294,37 @@ extern void tlb_flush_rmaps(struct mmu_gather *tlb, struct vm_area_struct *vma);
> >>>> static inline void tlb_flush_rmaps(struct mmu_gather *tlb, struct vm_area_struct *vma) { }
> >>>> #endif
> >>>>
> >>>> +#ifndef CONFIG_MMU_GATHER_NO_GATHER
> >>>> +struct mmu_swap_batch {
> >>>> + struct mmu_swap_batch *next;
> >>>> + unsigned int nr;
> >>>> + unsigned int max;
> >>>> + encoded_swpentry_t encoded_entrys[];
> >>>> +};
> >>>> +
> >>>> +#define MAX_SWAP_GATHER_BATCH \
> >>>> + ((PAGE_SIZE - sizeof(struct mmu_swap_batch)) / sizeof(void *))
> >>>> +
> >>>> +#define MAX_SWAP_GATHER_BATCH_COUNT (10000UL / MAX_SWAP_GATHER_BATCH)
> >>>> +
> >>>> +struct mmu_swap_gather {
> >>>> + /*
> >>>> + * the asynchronous kworker to batch
> >>>> + * release swap entries
> >>>> + */
> >>>> + struct work_struct free_work;
> >>>> +
> >>>> + /* batch cache swap entries */
> >>>> + unsigned int batch_count;
> >>>> + struct mmu_swap_batch *active;
> >>>> + struct mmu_swap_batch local;
> >>>> + encoded_swpentry_t __encoded_entrys[MMU_GATHER_BUNDLE];
> >>>> +};
> >>>> +
> >>>> +bool __tlb_remove_swap_entries(struct mmu_gather *tlb,
> >>>> + swp_entry_t entry, int nr);
> >>>> +#endif
> >>>> +
> >>>> /*
> >>>> * struct mmu_gather is an opaque type used by the mm code for passing around
> >>>> * any data needed by arch specific code for tlb_remove_page.
> >>>> @@ -343,6 +374,18 @@ struct mmu_gather {
> >>>> unsigned int vma_exec : 1;
> >>>> unsigned int vma_huge : 1;
> >>>> unsigned int vma_pfn : 1;
> >>>> +#ifndef CONFIG_MMU_GATHER_NO_GATHER
> >>>> + /*
> >>>> + * Two states of releasing swap entries
> >>>> + * asynchronously:
> >>>> + * swp_freeable - have opportunity to
> >>>> + * release asynchronously future
> >>>> + * swp_freeing - be releasing asynchronously.
> >>>> + */
> >>>> + unsigned int swp_freeable : 1;
> >>>> + unsigned int swp_freeing : 1;
> >>>> + unsigned int swp_disable : 1;
> >>>> +#endif
> >>>>
> >>>> unsigned int batch_count;
> >>>>
> >>>> @@ -354,6 +397,7 @@ struct mmu_gather {
> >>>> #ifdef CONFIG_MMU_GATHER_PAGE_SIZE
> >>>> unsigned int page_size;
> >>>> #endif
> >>>> + struct mmu_swap_gather *swp;
> >>>> #endif
> >>>> };
> >>>>
> >>>> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> >>>> index 165c58b12ccc..2f66303f1519
> >>>> --- a/include/linux/mm_types.h
> >>>> +++ b/include/linux/mm_types.h
> >>>> @@ -283,6 +283,64 @@ typedef struct {
> >>>> unsigned long val;
> >>>> } swp_entry_t;
> >>>>
> >>>> +/*
> >>>> + * encoded_swpentry_t - a type marking the encoded swp_entry_t.
> >>>> + *
> >>>> + * An 'encoded_swpentry_t' represents a 'swp_enrty_t' with its the highest
> >>>> + * bit indicating extra context-dependent information. Only used in swp_entry
> >>>> + * asynchronous release path by mmu_swap_gather.
> >>>> + */
> >>>> +typedef struct {
> >>>> + unsigned long val;
> >>>> +} encoded_swpentry_t;
> >>>> +
> >>>> +/*
> >>>> + * The next item in an encoded_swpentry_t array is the "nr" argument, specifying the
> >>>> + * total number of consecutive swap entries associated with the same folio. If this
> >>>> + * bit is not set, "nr" is implicitly 1.
> >>>> + *
> >>>> + * Refer to include\asm\pgtable.h, swp_offset bits: 0 ~ 57, swp_type bits: 58 ~ 62.
> >>>> + * Bit63 can be used here.
> >>>> + */
> >>>> +#define ENCODED_SWPENTRY_BIT_NR_ENTRYS_NEXT (1UL << (BITS_PER_LONG - 1))
> >>>> +
> >>>> +static __always_inline encoded_swpentry_t
> >>>> +encode_swpentry(swp_entry_t entry, unsigned long flags)
> >>>> +{
> >>>> + encoded_swpentry_t ret;
> >>>> +
> >>>> + VM_WARN_ON_ONCE(flags & ~ENCODED_SWPENTRY_BIT_NR_ENTRYS_NEXT);
> >>>> + ret.val = flags | entry.val;
> >>>> + return ret;
> >>>> +}
> >>>> +
> >>>> +static inline unsigned long encoded_swpentry_flags(encoded_swpentry_t entry)
> >>>> +{
> >>>> + return ENCODED_SWPENTRY_BIT_NR_ENTRYS_NEXT & entry.val;
> >>>> +}
> >>>> +
> >>>> +static inline swp_entry_t encoded_swpentry_data(encoded_swpentry_t entry)
> >>>> +{
> >>>> + swp_entry_t ret;
> >>>> +
> >>>> + ret.val = ~ENCODED_SWPENTRY_BIT_NR_ENTRYS_NEXT & entry.val;
> >>>> + return ret;
> >>>> +}
> >>>> +
> >>>> +static __always_inline encoded_swpentry_t encode_nr_swpentrys(unsigned long nr)
> >>>> +{
> >>>> + encoded_swpentry_t ret;
> >>>> +
> >>>> + VM_WARN_ON_ONCE(nr & ENCODED_SWPENTRY_BIT_NR_ENTRYS_NEXT);
> >>>> + ret.val = nr;
> >>>> + return ret;
> >>>> +}
> >>>> +
> >>>> +static __always_inline unsigned long encoded_nr_swpentrys(encoded_swpentry_t entry)
> >>>> +{
> >>>> + return ((~ENCODED_SWPENTRY_BIT_NR_ENTRYS_NEXT) & entry.val);
> >>>> +}
> >>>> +
> >>>> /**
> >>>> * struct folio - Represents a contiguous set of bytes.
> >>>> * @flags: Identical to the page flags.
> >>>> diff --git a/mm/memory.c b/mm/memory.c
> >>>> index d6a9dcddaca4..023a8adcb67c
> >>>> --- a/mm/memory.c
> >>>> +++ b/mm/memory.c
> >>>> @@ -1650,7 +1650,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
> >>>> if (!should_zap_cows(details))
> >>>> continue;
> >>>> rss[MM_SWAPENTS] -= nr;
> >>>> - free_swap_and_cache_nr(entry, nr);
> >>>> + if (!__tlb_remove_swap_entries(tlb, entry, nr))
> >>>> + free_swap_and_cache_nr(entry, nr);
> >>>> } else if (is_migration_entry(entry)) {
> >>>> folio = pfn_swap_entry_folio(entry);
> >>>> if (!should_zap_folio(details, folio))
> >>>> diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
> >>>> index 99b3e9408aa0..33dc9d1faff9
> >>>> --- a/mm/mmu_gather.c
> >>>> +++ b/mm/mmu_gather.c
> >>>> @@ -9,11 +9,303 @@
> >>>> #include <linux/smp.h>
> >>>> #include <linux/swap.h>
> >>>> #include <linux/rmap.h>
> >>>> +#include <linux/oom.h>
> >>>>
> >>>> #include <asm/pgalloc.h>
> >>>> #include <asm/tlb.h>
> >>>>
> >>>> #ifndef CONFIG_MMU_GATHER_NO_GATHER
> >>>> +/*
> >>>> + * The swp_entry asynchronous release mechanism for multiple processes with
> >>>> + * independent mm exiting simultaneously.
> >>>> + *
> >>>> + * During the multiple exiting processes releasing their own mm simultaneously,
> >>>> + * the swap entries in the exiting processes are handled by isolating, caching
> >>>> + * and handing over to an asynchronous kworker to complete the release.
> >>>> + *
> >>>> + * The conditions for the exiting process entering the swp_entry asynchronous
> >>>> + * release path:
> >>>> + * 1. The exiting process's MM_SWAPENTS count is >= SWAP_CLUSTER_MAX, avoiding
> >>>> + * to alloc struct mmu_swap_gather frequently.
> >>>> + * 2. The number of exiting processes is >= NR_MIN_EXITING_PROCESSES.
> >>> Hi Zhiguo,
> >>>
> >>> I'm curious about the significance of NR_MIN_EXITING_PROCESSES. It seems that
> >>> batched swap entry freeing, even with one process, could be a
> >>> bottleneck for a single
> >>> process based on the data from this patch:
> >>>
> >>> mm: attempt to batch free swap entries for zap_pte_range()
> >>> https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-stable&id=bea67dcc5ee
> >>> "munmap bandwidth becomes 3X faster."
> >>>
> >>> So what would happen if you simply set NR_MIN_EXITING_PROCESSES to 1?
> >> Hi Barry,
> >>
> >> Thanks for your comments.
> >>
> >> The reason for NR_MIN_EXITING_PROCESSES = 2 is that previously we
> >> conducted the multiple android apps continuous startup performance
> >> test on the case of NR_MIN_EXITING_PROCESSES = 1, and the results
> >> showed that the startup time had deteriorated slightly. However,
> >> the patch's logic in this test was different from the one I submitted
> >> to the community, and it may be due to some other issues with the
> >> previous old patch.
> >>
> >> However, we have conducted relevant memory performance tests on this
> >> patches submitted to the community (NR_MIN_EXITING_PROCESSES=2), and
> >> the results are better than before the modification. The patches have
> >> been used on multiple projects.
> >> For example:
> >> Test the time consumption and subjective fluency experience of
> >> launching 30 android apps continuously for two rounds.
> >> Test machine: RAM 16GB
> >> | | time(s) | Frame-droped rate(%) |
> >> | before | 230.76 | 0.54 |
> >> | after | 225.23 | 0.74 |
> >> We can see that the patch has been optimized 5.53s for startup time and
> >> 0.2% frame-droped rate and better subjective smoothness experience.
> >>
> >> Perhaps the patches submitted to the community has also improved the
> >> multiple android apps continuous startup performance in the case
> >> of NR_MIN_EXITING_PROCESSES=1. If necessary, I will conduct relevant
> >> tests to verify this situation in the future.
> Thanks Barry for your valuable suggestions.
> > Using a fixed value like 2 feels more like a workaround than a solid solution.
> > It would be better if we could eliminate this hack.
> Ok, I will conduct more tests for tring to solve this parameter issue.
> >
> > Additionally, this type of asynchronous reclamation might struggle to scale
> > effectively, particularly on NUMA systems with many CPU cores.
> >
> > Many kernel threads are per-node, like kswapd. For instance, if we have 100
> > threads running on 100 CPUs executing zap_pte_range(), your approach, which
> > relies on a single async thread to reclaim swap entries, might lead to
> > performance
> > regressions.
> >
> > We might need to consider a more adaptable approach that can evaluate
> > the machine's
> > topology and dynamically determine the appropriate number of async
> > threads, rather
> > than hard-coding it to just one. Otherwise, there could be ongoing
> > concerns about
> > whether this solution is truly applicable to all systems.
> Can we dynamically determine the number of asynchronous kworkers to be
> created based on the number of exiting processes at a certain moment,
> for example, every 8 exiting processes corresponds to one asynchronous
> kworker?
>
> | The number of exiting processes | The number of asynchronous kworkers |
> | [1, 8] | 1 |
> | [9, 16] | 2 |
> | ... | ... |
> | [8*N+1, 8*(N+1)] | N+1 |
> N >= 0

I'm not entirely sure. Another potential approach could be to use a
dedicated thread
for each NUMA node, but we would need data to confirm if this is the
right solution.

> > Alternatively, we might be able to develop a method to speed up
> > batched freeing in a
> > synchronous manner after collecting the mmu_swap_batch. mmu_gather isn't
> > async, but it can still speed up tlb flush, right?
> The synchronous manner may have some optimization effect, but it seems
> that the optimization effect on the CPUs load occupied by multiple
> exiting processes is not significant. In addition, David stated in the
> latest comment that swap entry seems unrelated to tlb.
> > For phones with just 8 CPU cores, I definitely like your patch.
> > However, since we're
> > aiming for something which can affect all systems, the situation might be more
> > complex.
> Yes, this pacth still needs further improvement to adapt to all systems.

If we want to keep things simple, another approach might be to profile the
hotspots within swap_free_nr(), identifying the most time-consuming parts,
and then optimize them based on the data we collect from your
mmu_swap_batch. Then we don't have to make things async. Have you ever
profiled the hotspots?

> >>>> + *
> >>>> + * Since the time for determining the number of exiting processes is dynamic,
> >>>> + * the exiting process may start to enter the swp_entry asynchronous release
> >>>> + * at the beginning or middle stage of the exiting process's swp_entry release
> >>>> + * path.
> >>>> + *
> >>>> + * Once an exiting process enters the swp_entry asynchronous release, all remaining
> >>>> + * swap entries in this exiting process need to be fully released by asynchronous
> >>>> + * kworker theoretically.
> >>> Freeing a slot can indeed release memory from `zRAM`, potentially returning
> >>> it to the system for allocation. Your patch frees swap slots asynchronously;
> >>> I assume this doesn’t slow down the memory freeing process for `zRAM`, or
> >>> could it even slow down the freeing of `zRAM` memory? Freeing compressed
> >>> memory might not be as crucial compared to freeing uncompressed memory with
> >>> present PTEs?
> >> Yes, freeing uncompressed memory with present PTEs is more important
> >> compared to freeing compressed 'zRAM' memory.
> >>
> >> I guess that the multiple exiting processes releasing swap entries
> >> simultaneously may result in the swap_info->lock competition pressure
> >> in swapcache_free_entries(), affecting the efficiency of releasing swap
> >> entries. However, if the asynchronous kworker is used, this issue can
> >> be avoided, and perhaps the improvement is minor.
> >>
> >> The freeing of zRAM memory does not slow down. We have observed traces
> >> in the camera startup scene and found that the asynchronous kworker
> >> can release all swap entries before entering the camera preview.
> >> Compared to not using the asynchronous kworker, the exiting processes
> >> completed after entering the camera preview.
> >>>> + *
> >>>> + * The function of the swp_entry asynchronous release:
> >>>> + * 1. Alleviate the high system cpu load 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.
> >>>> + */
> >>>> +
> >>>> +/*
> >>>> + * The min number of exiting processes required for swp_entry asynchronous release
> >>>> + */
> >>>> +#define NR_MIN_EXITING_PROCESSES 2
> >>>> +
> >>>> +static atomic_t nr_exiting_processes = ATOMIC_INIT(0);
> >>>> +static struct kmem_cache *swap_gather_cachep;
> >>>> +static struct workqueue_struct *swapfree_wq;
> >>>> +static DEFINE_STATIC_KEY_TRUE(tlb_swap_asyncfree_disabled);
> >>>> +
> >>>> +static int __init tlb_swap_async_free_setup(void)
> >>>> +{
> >>>> + swapfree_wq = alloc_workqueue("smfree_wq", WQ_UNBOUND |
> >>>> + WQ_HIGHPRI | WQ_MEM_RECLAIM, 1);
> >>>> + if (!swapfree_wq)
> >>>> + goto fail;
> >>>> +
> >>>> + swap_gather_cachep = kmem_cache_create("swap_gather",
> >>>> + sizeof(struct mmu_swap_gather),
> >>>> + 0, SLAB_TYPESAFE_BY_RCU | SLAB_PANIC | SLAB_ACCOUNT,
> >>>> + NULL);
> >>>> + if (!swap_gather_cachep)
> >>>> + goto kcache_fail;
> >>>> +
> >>>> + static_branch_disable(&tlb_swap_asyncfree_disabled);
> >>>> + return 0;
> >>>> +
> >>>> +kcache_fail:
> >>>> + destroy_workqueue(swapfree_wq);
> >>>> +fail:
> >>>> + return -ENOMEM;
> >>>> +}
> >>>> +postcore_initcall(tlb_swap_async_free_setup);
> >>>> +
> >>>> +static void __tlb_swap_gather_free(struct mmu_swap_gather *swap_gather)
> >>>> +{
> >>>> + struct mmu_swap_batch *swap_batch, *next;
> >>>> +
> >>>> + for (swap_batch = swap_gather->local.next; swap_batch; swap_batch = next) {
> >>>> + next = swap_batch->next;
> >>>> + free_page((unsigned long)swap_batch);
> >>>> + }
> >>>> + swap_gather->local.next = NULL;
> >>>> + kmem_cache_free(swap_gather_cachep, swap_gather);
> >>>> +}
> >>>> +
> >>>> +static void tlb_swap_async_free_work(struct work_struct *w)
> >>>> +{
> >>>> + int i, nr_multi, nr_free;
> >>>> + swp_entry_t start_entry;
> >>>> + struct mmu_swap_batch *swap_batch;
> >>>> + struct mmu_swap_gather *swap_gather = container_of(w,
> >>>> + struct mmu_swap_gather, free_work);
> >>>> +
> >>>> + /* Release swap entries cached in mmu_swap_batch. */
> >>>> + for (swap_batch = &swap_gather->local; swap_batch && swap_batch->nr;
> >>>> + swap_batch = swap_batch->next) {
> >>>> + nr_free = 0;
> >>>> + for (i = 0; i < swap_batch->nr; i++) {
> >>>> + if (unlikely(encoded_swpentry_flags(swap_batch->encoded_entrys[i]) &
> >>>> + ENCODED_SWPENTRY_BIT_NR_ENTRYS_NEXT)) {
> >>>> + start_entry = encoded_swpentry_data(swap_batch->encoded_entrys[i]);
> >>>> + nr_multi = encoded_nr_swpentrys(swap_batch->encoded_entrys[++i]);
> >>>> + free_swap_and_cache_nr(start_entry, nr_multi);
> >>>> + nr_free += 2;
> >>>> + } else {
> >>>> + start_entry = encoded_swpentry_data(swap_batch->encoded_entrys[i]);
> >>>> + free_swap_and_cache_nr(start_entry, 1);
> >>>> + nr_free++;
> >>>> + }
> >>>> + }
> >>>> + swap_batch->nr -= nr_free;
> >>>> + VM_BUG_ON(swap_batch->nr);
> >>>> + }
> >>>> + __tlb_swap_gather_free(swap_gather);
> >>>> +}
> >>>> +
> >>>> +static bool __tlb_swap_gather_mmu_check(struct mmu_gather *tlb)
> >>>> +{
> >>>> + /*
> >>>> + * Only the exiting processes with the MM_SWAPENTS counter >=
> >>>> + * SWAP_CLUSTER_MAX have the opportunity to release their swap
> >>>> + * entries by asynchronous kworker.
> >>>> + */
> >>>> + if (!task_is_dying() ||
> >>>> + get_mm_counter(tlb->mm, MM_SWAPENTS) < SWAP_CLUSTER_MAX)
> >>>> + return true;
> >>>> +
> >>>> + atomic_inc(&nr_exiting_processes);
> >>>> + if (atomic_read(&nr_exiting_processes) < NR_MIN_EXITING_PROCESSES)
> >>>> + tlb->swp_freeable = 1;
> >>>> + else
> >>>> + tlb->swp_freeing = 1;
> >>>> +
> >>>> + return false;
> >>>> +}
> >>>> +
> >>>> +/**
> >>>> + * __tlb_swap_gather_init - Initialize an mmu_swap_gather structure
> >>>> + * for swp_entry tear-down.
> >>>> + * @tlb: the mmu_swap_gather structure belongs to tlb
> >>>> + */
> >>>> +static bool __tlb_swap_gather_init(struct mmu_gather *tlb)
> >>>> +{
> >>>> + tlb->swp = kmem_cache_alloc(swap_gather_cachep, GFP_ATOMIC | GFP_NOWAIT);
> >>>> + if (unlikely(!tlb->swp))
> >>>> + return false;
> >>>> +
> >>>> + tlb->swp->local.next = NULL;
> >>>> + tlb->swp->local.nr = 0;
> >>>> + tlb->swp->local.max = ARRAY_SIZE(tlb->swp->__encoded_entrys);
> >>>> +
> >>>> + tlb->swp->active = &tlb->swp->local;
> >>>> + tlb->swp->batch_count = 0;
> >>>> +
> >>>> + INIT_WORK(&tlb->swp->free_work, tlb_swap_async_free_work);
> >>>> + return true;
> >>>> +}
> >>>> +
> >>>> +static void __tlb_swap_gather_mmu(struct mmu_gather *tlb)
> >>>> +{
> >>>> + if (static_branch_unlikely(&tlb_swap_asyncfree_disabled))
> >>>> + return;
> >>>> +
> >>>> + tlb->swp = NULL;
> >>>> + tlb->swp_freeable = 0;
> >>>> + tlb->swp_freeing = 0;
> >>>> + tlb->swp_disable = 0;
> >>>> +
> >>>> + if (__tlb_swap_gather_mmu_check(tlb))
> >>>> + return;
> >>>> +
> >>>> + /*
> >>>> + * If the exiting process meets the conditions of
> >>>> + * swp_entry asynchronous release, an mmu_swap_gather
> >>>> + * structure will be initialized.
> >>>> + */
> >>>> + if (tlb->swp_freeing)
> >>>> + __tlb_swap_gather_init(tlb);
> >>>> +}
> >>>> +
> >>>> +static void __tlb_swap_gather_queuework(struct mmu_gather *tlb, bool finish)
> >>>> +{
> >>>> + queue_work(swapfree_wq, &tlb->swp->free_work);
> >>>> + tlb->swp = NULL;
> >>>> + if (!finish)
> >>>> + __tlb_swap_gather_init(tlb);
> >>>> +}
> >>>> +
> >>>> +static bool __tlb_swap_next_batch(struct mmu_gather *tlb)
> >>>> +{
> >>>> + struct mmu_swap_batch *swap_batch;
> >>>> +
> >>>> + if (tlb->swp->batch_count == MAX_SWAP_GATHER_BATCH_COUNT)
> >>>> + goto free;
> >>>> +
> >>>> + swap_batch = (void *)__get_free_page(GFP_ATOMIC | GFP_NOWAIT);
> >>>> + if (unlikely(!swap_batch))
> >>>> + goto free;
> >>>> +
> >>>> + swap_batch->next = NULL;
> >>>> + swap_batch->nr = 0;
> >>>> + swap_batch->max = MAX_SWAP_GATHER_BATCH;
> >>>> +
> >>>> + tlb->swp->active->next = swap_batch;
> >>>> + tlb->swp->active = swap_batch;
> >>>> + tlb->swp->batch_count++;
> >>>> + return true;
> >>>> +free:
> >>>> + /* batch move to wq */
> >>>> + __tlb_swap_gather_queuework(tlb, false);
> >>>> + return false;
> >>>> +}
> >>>> +
> >>>> +/**
> >>>> + * __tlb_remove_swap_entries - the swap entries in exiting process are
> >>>> + * isolated, batch cached in struct mmu_swap_batch.
> >>>> + * @tlb: the current mmu_gather
> >>>> + * @entry: swp_entry to be isolated and cached
> >>>> + * @nr: the number of consecutive entries starting from entry parameter.
> >>>> + */
> >>>> +bool __tlb_remove_swap_entries(struct mmu_gather *tlb,
> >>>> + swp_entry_t entry, int nr)
> >>>> +{
> >>>> + struct mmu_swap_batch *swap_batch;
> >>>> + unsigned long flags = 0;
> >>>> + bool ret = false;
> >>>> +
> >>>> + if (tlb->swp_disable)
> >>>> + return ret;
> >>>> +
> >>>> + if (!tlb->swp_freeable && !tlb->swp_freeing)
> >>>> + return ret;
> >>>> +
> >>>> + if (tlb->swp_freeable) {
> >>>> + if (atomic_read(&nr_exiting_processes) <
> >>>> + NR_MIN_EXITING_PROCESSES)
> >>>> + return ret;
> >>>> + /*
> >>>> + * If the current number of exiting processes
> >>>> + * is >= NR_MIN_EXITING_PROCESSES, the exiting
> >>>> + * process with swp_freeable state will enter
> >>>> + * swp_freeing state to start releasing its
> >>>> + * remaining swap entries by the asynchronous
> >>>> + * kworker.
> >>>> + */
> >>>> + tlb->swp_freeable = 0;
> >>>> + tlb->swp_freeing = 1;
> >>>> + }
> >>>> +
> >>>> + VM_BUG_ON(tlb->swp_freeable || !tlb->swp_freeing);
> >>>> + if (!tlb->swp && !__tlb_swap_gather_init(tlb))
> >>>> + return ret;
> >>>> +
> >>>> + swap_batch = tlb->swp->active;
> >>>> + if (unlikely(swap_batch->nr >= swap_batch->max - 1)) {
> >>>> + __tlb_swap_gather_queuework(tlb, false);
> >>>> + return ret;
> >>>> + }
> >>>> +
> >>>> + if (likely(nr == 1)) {
> >>>> + swap_batch->encoded_entrys[swap_batch->nr++] = encode_swpentry(entry, flags);
> >>>> + } else {
> >>>> + flags |= ENCODED_SWPENTRY_BIT_NR_ENTRYS_NEXT;
> >>>> + swap_batch->encoded_entrys[swap_batch->nr++] = encode_swpentry(entry, flags);
> >>>> + swap_batch->encoded_entrys[swap_batch->nr++] = encode_nr_swpentrys(nr);
> >>>> + }
> >>>> + ret = true;
> >>>> +
> >>>> + if (swap_batch->nr >= swap_batch->max - 1) {
> >>>> + if (!__tlb_swap_next_batch(tlb))
> >>>> + goto exit;
> >>>> + swap_batch = tlb->swp->active;
> >>>> + }
> >>>> + VM_BUG_ON(swap_batch->nr > swap_batch->max - 1);
> >>>> +exit:
> >>>> + return ret;
> >>>> +}
> >>>> +
> >>>> +static void __tlb_batch_swap_finish(struct mmu_gather *tlb)
> >>>> +{
> >>>> + if (tlb->swp_disable)
> >>>> + return;
> >>>> +
> >>>> + if (!tlb->swp_freeable && !tlb->swp_freeing)
> >>>> + return;
> >>>> +
> >>>> + if (tlb->swp_freeable) {
> >>>> + tlb->swp_freeable = 0;
> >>>> + VM_BUG_ON(tlb->swp_freeing);
> >>>> + goto exit;
> >>>> + }
> >>>> + tlb->swp_freeing = 0;
> >>>> + if (unlikely(!tlb->swp))
> >>>> + goto exit;
> >>>> +
> >>>> + __tlb_swap_gather_queuework(tlb, true);
> >>>> +exit:
> >>>> + atomic_dec(&nr_exiting_processes);
> >>>> +}
> >>>>
> >>>> static bool tlb_next_batch(struct mmu_gather *tlb)
> >>>> {
> >>>> @@ -386,6 +678,9 @@ static void __tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
> >>>> tlb->local.max = ARRAY_SIZE(tlb->__pages);
> >>>> tlb->active = &tlb->local;
> >>>> tlb->batch_count = 0;
> >>>> +
> >>>> + tlb->swp_disable = 1;
> >>>> + __tlb_swap_gather_mmu(tlb);
> >>>> #endif
> >>>> tlb->delayed_rmap = 0;
> >>>>
> >>>> @@ -466,6 +761,7 @@ void tlb_finish_mmu(struct mmu_gather *tlb)
> >>>>
> >>>> #ifndef CONFIG_MMU_GATHER_NO_GATHER
> >>>> tlb_batch_list_free(tlb);
> >>>> + __tlb_batch_swap_finish(tlb);
> >>>> #endif
> >>>> dec_tlb_flush_pending(tlb->mm);
> >>>> }
> >>>> --
> >>>> 2.39.0
> >>>>
> > Thanks
> > Barry
> Thanks
> Zhiguo
>

Thanks
Barry

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