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If the AS_WRITEBACK_INDETERMINATE flag is set on the mapping,= the >> writeback may take an indeterminate amount of time to complete, and >> waits may get stuck. >> >> Signed-off-by: Joanne Koong >> Reviewed-by: Shakeel Butt >> --- >> mm/migrate.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index df91248755e4..fe73284e5246 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1260,7 +1260,10 @@ static int migrate_folio_unmap(new_folio_t get_= new_folio, >> */ >> switch (mode) { >> case MIGRATE_SYNC: >> - break; >> + if (!src->mapping || >> + !mapping_writeback_indeterminate(src->mapping)) >> + break; >> + fallthrough; >> default: >> rc =3D -EBUSY; >> goto out; > > Ehm, doesn't this mean that any fuse user can essentially completely bl= ock CMA allocations, memory compaction, memory hotunplug, memory poisonin= g... ?! > > That sounds very bad. Yeah, these writeback folios become unmovable. It makes memory fragmentat= ion unrecoverable. I do not know why AS_WRITEBACK_INDETERMINATE is allowed, s= ince it is essentially a forever pin to writeback folios. Why not introduce a retry and timeout mechanism instead of waiting for the writeback forever?= -- Best Regards, Yan, Zi