On 6/18/26 02:57, Vlastimil Babka (SUSE) wrote:
> On 6/4/26 04:38, Wandun Chen wrote:
>> From: Wandun Chen <[email protected]>
>>
>> vm.compact_unevictable_allowed=0 is used to prevent compacting
>> unevictable pages. However, isolate_migratepages_range() passes
>> ISOLATE_UNEVICTABLE regardless of this sysctl, so the setting
>> has no effect in the alloc_contig path.
>>
>> Fix it by:
>> - Keep ISOLATE_UNEVICTABLE for CMA allocation, discussed in [1].
>> - Honour sysctl_compact_unevictable_allowed for non-CMA allocation.
>>
>> Suggested-by: Vlastimil Babka <[email protected]>
>> Signed-off-by: Wandun Chen <[email protected]>
>> Link:
>> https://lore.kernel.org/all/[email protected]/ [1]
>
> There was also the "Ideally by not having mlock'd pages in CMA areas at
> all." part. Is it the case? It was more elaborated here:
Yes, It is the case.
> https://lore.kernel.org/all/CAPTztWZpnX1j8-7yeppVUsxE=o9hbveqricdjzt8_pnn7a-...@mail.gmail.com/
I missed this important information. Thanks for pointing it out, Vlastimil.
Best regards,
Wandun
>
>> ---
>> include/linux/compaction.h | 6 ++++++
>> mm/compaction.c | 9 +++++++--
>> mm/internal.h | 1 +
>> mm/page_alloc.c | 2 ++
>> 4 files changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
>> index f29ef0653546..04e60f65b976 100644
>> --- a/include/linux/compaction.h
>> +++ b/include/linux/compaction.h
>> @@ -106,6 +106,7 @@ bool compaction_zonelist_suitable(struct alloc_context
>> *ac, int order,
>> extern void __meminit kcompactd_run(int nid);
>> extern void __meminit kcompactd_stop(int nid);
>> extern void wakeup_kcompactd(pg_data_t *pgdat, int order, int
>> highest_zoneidx);
>> +extern bool compaction_allow_unevictable(void);
>>
>> #else
>> static inline void reset_isolation_suitable(pg_data_t *pgdat)
>> @@ -131,6 +132,11 @@ static inline void wakeup_kcompactd(pg_data_t *pgdat,
>> {
>> }
>>
>> +static inline bool compaction_allow_unevictable(void)
>> +{
>> + return true;
>> +}
>> +
>> #endif /* CONFIG_COMPACTION */
>>
>> struct node;
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 007d5e00a8ae..a10acb273454 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -1341,6 +1341,7 @@ isolate_migratepages_range(struct compact_control *cc,
>> unsigned long start_pfn,
>> unsigned long end_pfn)
>> {
>> unsigned long pfn, block_start_pfn, block_end_pfn;
>> + isolate_mode_t mode = cc->allow_unevictable ? ISOLATE_UNEVICTABLE : 0;
>> int ret = 0;
>>
>> /* Scan block by block. First and last block may be incomplete */
>> @@ -1360,8 +1361,7 @@ isolate_migratepages_range(struct compact_control *cc,
>> unsigned long start_pfn,
>> block_end_pfn, cc->zone))
>> continue;
>>
>> - ret = isolate_migratepages_block(cc, pfn, block_end_pfn,
>> - ISOLATE_UNEVICTABLE);
>> + ret = isolate_migratepages_block(cc, pfn, block_end_pfn, mode);
>>
>> if (ret)
>> break;
>> @@ -1902,6 +1902,11 @@ typedef enum {
>> * compactable pages.
>> */
>> static int sysctl_compact_unevictable_allowed __read_mostly =
>> CONFIG_COMPACT_UNEVICTABLE_DEFAULT;
>> +
>> +bool compaction_allow_unevictable(void)
>> +{
>> + return sysctl_compact_unevictable_allowed;
>> +}
>> /*
>> * Tunable for proactive compaction. It determines how
>> * aggressively the kernel should compact memory in the
>> diff --git a/mm/internal.h b/mm/internal.h
>> index 181e79f1d6a2..163f9d6b37f3 100644
>> --- a/mm/internal.h
>> +++ b/mm/internal.h
>> @@ -1052,6 +1052,7 @@ struct compact_control {
>> * ensure forward progress.
>> */
>> bool alloc_contig; /* alloc_contig_range allocation */
>> + bool allow_unevictable; /* Allow isolation of unevictable
>> folios */
>> };
>>
>> /*
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 81a9d4d1e6c0..1cf9d4a3b14c 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -7118,6 +7118,8 @@ int alloc_contig_frozen_range_noprof(unsigned long
>> start, unsigned long end,
>> .ignore_skip_hint = true,
>> .no_set_skip_hint = true,
>> .alloc_contig = true,
>> + .allow_unevictable = !!(alloc_flags & ACR_FLAGS_CMA) ||
>> + compaction_allow_unevictable(),
>> };
>> INIT_LIST_HEAD(&cc.migratepages);
>> enum pb_isolate_mode mode = (alloc_flags & ACR_FLAGS_CMA) ?
>
