diff options
Diffstat (limited to 'Documentation/vm')
| -rw-r--r-- | Documentation/vm/unevictable-lru.txt | 8 | ||||
| -rw-r--r-- | Documentation/vm/zswap.txt | 18 |
2 files changed, 23 insertions, 3 deletions
diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt index 3be0bfc47..32ee3a67d 100644 --- a/Documentation/vm/unevictable-lru.txt +++ b/Documentation/vm/unevictable-lru.txt @@ -467,7 +467,13 @@ mmap(MAP_LOCKED) SYSTEM CALL HANDLING In addition the mlock()/mlockall() system calls, an application can request that a region of memory be mlocked supplying the MAP_LOCKED flag to the mmap() -call. Furthermore, any mmap() call or brk() call that expands the heap by a +call. There is one important and subtle difference here, though. mmap() + mlock() +will fail if the range cannot be faulted in (e.g. because mm_populate fails) +and returns with ENOMEM while mmap(MAP_LOCKED) will not fail. The mmaped +area will still have properties of the locked area - aka. pages will not get +swapped out - but major page faults to fault memory in might still happen. + +Furthermore, any mmap() call or brk() call that expands the heap by a task that has previously called mlockall() with the MCL_FUTURE flag will result in the newly mapped memory being mlocked. Before the unevictable/mlock changes, the kernel simply called make_pages_present() to allocate pages and diff --git a/Documentation/vm/zswap.txt b/Documentation/vm/zswap.txt index 00c3d31e7..8458c0861 100644 --- a/Documentation/vm/zswap.txt +++ b/Documentation/vm/zswap.txt @@ -26,8 +26,22 @@ Zswap evicts pages from compressed cache on an LRU basis to the backing swap device when the compressed pool reaches its size limit. This requirement had been identified in prior community discussions. -To enabled zswap, the "enabled" attribute must be set to 1 at boot time. e.g. -zswap.enabled=1 +Zswap is disabled by default but can be enabled at boot time by setting +the "enabled" attribute to 1 at boot time. ie: zswap.enabled=1. Zswap +can also be enabled and disabled at runtime using the sysfs interface. +An example command to enable zswap at runtime, assuming sysfs is mounted +at /sys, is: + +echo 1 > /sys/modules/zswap/parameters/enabled + +When zswap is disabled at runtime it will stop storing pages that are +being swapped out. However, it will _not_ immediately write out or fault +back into memory all of the pages stored in the compressed pool. The +pages stored in zswap will remain in the compressed pool until they are +either invalidated or faulted back into memory. In order to force all +pages out of the compressed pool, a swapoff on the swap device(s) will +fault back into memory all swapped out pages, including those in the +compressed pool. Design: |