This series attempts to rework the mlock_count tracking scheme to avoid overlaying page->lru. The main goal is to revive the unevictable LRU, which would be useful for upcoming work for offline memcgs recharging [1]. For that work, we need to be able to find all the pages charged to a memcg, and iterating the LRUS is the most efficient way to do it. With the current mlock_count scheme, the unevictable LRU is imaginary, as page->mlock_count overlays page->lru. The proposed scheme overloads page->_mapcount to track mlock_count for order-0 pages, slightly similar to how page->_refcount is overloaded for pincount. More details in patch 1. Another advantage of this series is that we do not have to reset the mlock_count everytime we isolate an mlocked page from the LRU. This means we can more reliably track the mlock_count -- we are less likely to prematurely munlock() a page. We also do not need to re-initialize the mlock_count every time we add an mlocked page to the LRUs, or every time we found that it was reset during mlock/munlock. The lack of re-initialization slightly simplifies the mlock_count logic. The complexity is also more contained within mm/mlock.c. This series is based on v6.4-rc6, and has been tested with the mlock selftests (though I had to rebase to v6.2 to get those selftests working). The series is broken up as follows: - Patch 1 is the actual rework of the mlock_count scheme. - Patch 2 handles the case where a page might be mistaknely stranded as mlocked indefinetly if it was mapped a very large number of times. - Patch 3 adds a WARN_ON() in case a very large number of mappings can be mistakenly interpreted as an mlock_count. - Patch 4 revives the unevictable LRU. - Patch 5 reverts a patch that was part of the original mlock_count series [2] that is no longer needed now. [1]https://lore.kernel.org/linux-mm/CAJD7tkb56gR0X5v3VHfmk3az3bOz=wF2jhEi+7Eek0J8XXBeWQ@xxxxxxxxxxxxxx/ [2]https://lore.kernel.org/linux-mm/55a49083-37f9-3766-1de9-9feea7428ac@xxxxxxxxxx/ Yosry Ahmed (5): mm/mlock: rework mlock_count to use _mapcount for order-0 folios mm/mlock: fixup mlock_count during unmap mm/mlock: WARN_ON() if mapcount overflows into mlock_count mm/vmscan: revive the unevictable LRU Revert "mm/migrate: __unmap_and_move() push good newpage to LRU" include/linux/mm.h | 31 ++++++-- include/linux/mm_inline.h | 11 +-- include/linux/mm_types.h | 24 +----- mm/huge_memory.c | 5 +- mm/migrate.c | 24 +++--- mm/mlock.c | 150 +++++++++++++++++++++++++++++++++----- mm/mmzone.c | 8 -- mm/rmap.c | 3 + mm/swap.c | 8 -- 9 files changed, 174 insertions(+), 90 deletions(-) -- 2.41.0.162.gfafddb0af9-goog
