Re: [PATCH v1 1/3] mm: process_mrelease: expedite clean file folio reclaim via mmu_gather

David Hildenbrand (Arm)
2026-04-27T09:29:20Z

On 4/24/26 23:24, Minchan Kim wrote:
> On Fri, Apr 24, 2026 at 09:56:01AM +0200, David Hildenbrand (Arm) wrote:
>> On 4/22/26 01:02, Minchan Kim wrote:
>>
>> Can we make the subject easier to understand?
>>
>> "mm: process_mrelease: evict clean file folios when reaping a process"
>>
>>> Currently, process_mrelease() unmaps pages but file-backed pages are
>>> not evicted and stay in the pagecache, relying on standard memory reclaim
>>> (kswapd or direct reclaim) to eventually free them. This delays the
>>> immediate recovery of system memory under Android's LMKD scenarios,
>>> leading to redundant background apps kills.
>>>
>>> This patch implements an expedited eviction mechanism for clean pagecache
>>> folios in the mmu_gather code, similar to how swapcache folios are handled.
>>> It drops them from the pagecache (i.e., evicting them) if they are completely
>>> unmapped during reaping.
>>>
>>> Within this single unified loop, anonymous pages are released via
>>> free_swap_cache(), and file-backed folios are symmetrically released via
>>> free_file_cache().
>>>
>>> Signed-off-by: Minchan Kim <minchan@kernel.org>
>>> ---
>>> arch/s390/include/asm/tlb.h | 2 +-
>>> include/linux/swap.h | 5 ++---
>>> mm/mmu_gather.c | 7 ++++---
>>> mm/swap.c | 42 +++++++++++++++++++++++++++++++++++++
>>> mm/swap_state.c | 26 -----------------------
>>> 5 files changed, 49 insertions(+), 33 deletions(-)
>>>
>>> diff --git a/arch/s390/include/asm/tlb.h b/arch/s390/include/asm/tlb.h
>>> index 619fd41e710e..2736dbb571a8 100644
>>> --- a/arch/s390/include/asm/tlb.h
>>> +++ b/arch/s390/include/asm/tlb.h
>>> @@ -62,7 +62,7 @@ static inline bool __tlb_remove_folio_pages(struct mmu_gather *tlb,
>>> VM_WARN_ON_ONCE(delay_rmap);
>>> VM_WARN_ON_ONCE(page_folio(page) != page_folio(page + nr_pages - 1));
>>>
>>> - free_pages_and_swap_cache(encoded_pages, ARRAY_SIZE(encoded_pages));
>>> + free_pages_and_caches(tlb->mm, encoded_pages, ARRAY_SIZE(encoded_pages));
>>> return false;
>>> }
>>>
>>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>>> index 62fc7499b408..bdb784966343 100644
>>> --- a/include/linux/swap.h
>>> +++ b/include/linux/swap.h
>>> @@ -414,7 +414,9 @@ extern int sysctl_min_unmapped_ratio;
>>> extern int sysctl_min_slab_ratio;
>>> #endif
>>>
>>> +struct mm_struct;
>>> void check_move_unevictable_folios(struct folio_batch *fbatch);
>>> +void free_pages_and_caches(struct mm_struct *mm, struct encoded_page **pages, int nr);
>>>
>>> extern void __meminit kswapd_run(int nid);
>>> extern void __meminit kswapd_stop(int nid);
>>> @@ -433,7 +435,6 @@ static inline unsigned long total_swapcache_pages(void)
>>>
>>> void free_swap_cache(struct folio *folio);
>>> void free_folio_and_swap_cache(struct folio *folio);
>>> -void free_pages_and_swap_cache(struct encoded_page **, int);
>>> /* linux/mm/swapfile.c */
>>> extern atomic_long_t nr_swap_pages;
>>> extern long total_swap_pages;
>>> @@ -510,8 +511,6 @@ static inline void put_swap_device(struct swap_info_struct *si)
>>> do { (val)->freeswap = (val)->totalswap = 0; } while (0)
>>> #define free_folio_and_swap_cache(folio) \
>>> folio_put(folio)
>>> -#define free_pages_and_swap_cache(pages, nr) \
>>> - release_pages((pages), (nr));
>>>
>>> static inline void free_swap_cache(struct folio *folio)
>>> {
>>> diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
>>> index fe5b6a031717..3c6c315d3c48 100644
>>> --- a/mm/mmu_gather.c
>>> +++ b/mm/mmu_gather.c
>>> @@ -100,7 +100,8 @@ void tlb_flush_rmaps(struct mmu_gather *tlb, struct vm_area_struct *vma)
>>> */
>>> #define MAX_NR_FOLIOS_PER_FREE 512
>>>
>>> -static void __tlb_batch_free_encoded_pages(struct mmu_gather_batch *batch)
>>> +static void __tlb_batch_free_encoded_pages(struct mm_struct *mm,
>>> + struct mmu_gather_batch *batch)
>>> {
>>> struct encoded_page **pages = batch->encoded_pages;
>>> unsigned int nr, nr_pages;
>>> @@ -135,7 +136,7 @@ static void __tlb_batch_free_encoded_pages(struct mmu_gather_batch *batch)
>>> }
>>> }
>>>
>>> - free_pages_and_swap_cache(pages, nr);
>>> + free_pages_and_caches(mm, pages, nr);
>>> pages += nr;
>>> batch->nr -= nr;
>>>
>>> @@ -148,7 +149,7 @@ static void tlb_batch_pages_flush(struct mmu_gather *tlb)
>>> struct mmu_gather_batch *batch;
>>>
>>> for (batch = &tlb->local; batch && batch->nr; batch = batch->next)
>>> - __tlb_batch_free_encoded_pages(batch);
>>> + __tlb_batch_free_encoded_pages(tlb->mm, batch);
>>> tlb->active = &tlb->local;
>>> }
>>>
>>> diff --git a/mm/swap.c b/mm/swap.c
>>> index bb19ccbece46..e44bc8cefceb 100644
>>> --- a/mm/swap.c
>>> +++ b/mm/swap.c
>>> @@ -1043,6 +1043,48 @@ void release_pages(release_pages_arg arg, int nr)
>>> }
>>> EXPORT_SYMBOL(release_pages);
>>>
>>> +static inline void free_file_cache(struct folio *folio)
>>> +{
>>> + if (folio_trylock(folio)) {
>>> + mapping_evict_folio(folio_mapping(folio), folio);
>>> + folio_unlock(folio);
>>> + }
>>> +}
>>> +
>>> +/*
>>> + * Passed an array of pages, drop them all from swapcache and then release
>>> + * them. They are removed from the LRU and freed if this is their last use.
>>> + *
>>> + * If @try_evict_file_folios is true, this function will proactively evict clean
>>> + * file-backed folios if they are no longer mapped.
>>
>> There is no such parameter.
>>
>> But I do wonder if such a parameter would be better than passing in the MM here.
>
> Makes sense.
>
>>
>> Also, is there a way to avoid moving the function?
>
> I guess you are talking about "free_pages_and_swap_cache".
>
> The problem is mm/swap_state.c is conditionally compiled only when CONFIG_SWAP
> is enabled.
>
> Since the expedited clean file cache eviction should be available
> even on !CONFIG_SWAP, we need this function to be compiled unconditionally.
> That is why I moved it to swap.c, which is always compiled.

Ah, right. Please spell that out in the patch description!

--
Cheers,

David