Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
---
Documentation/vm/unevictable-lru.txt | 117 +++++++++++++++--------------------
1 file changed, 49 insertions(+), 68 deletions(-)
diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt
index e147185..fdd84cb 100644
--- a/Documentation/vm/unevictable-lru.txt
+++ b/Documentation/vm/unevictable-lru.txt
@@ -1,37 +1,13 @@
- ==============================
- UNEVICTABLE LRU INFRASTRUCTURE
- ==============================
-
-========
-CONTENTS
-========
-
- (*) The Unevictable LRU
-
- - The unevictable page list.
- - Memory control group interaction.
- - Marking address spaces unevictable.
- - Detecting Unevictable Pages.
- - vmscan's handling of unevictable pages.
-
- (*) mlock()'d pages.
-
- - History.
- - Basic management.
- - mlock()/mlockall() system call handling.
- - Filtering special vmas.
- - munlock()/munlockall() system call handling.
- - Migrating mlocked pages.
- - Compacting mlocked pages.
- - mmap(MAP_LOCKED) system call handling.
- - munmap()/exit()/exec() system call handling.
- - try_to_unmap().
- - try_to_munlock() reverse map scan.
- - Page reclaim in shrink_*_list().
+.. _unevictable_lru:
+==============================
+Unevictable LRU Infrastructure
+==============================
-============
-INTRODUCTION
+.. contents:: :local:
+
+
+Introduction
============
This document describes the Linux memory manager's "Unevictable LRU"
@@ -46,8 +22,8 @@ details - the "what does it do?" - by reading the code. One hopes that the
descriptions below add value by provide the answer to "why does it do that?".
-===================
-THE UNEVICTABLE LRU
+
+The Unevictable LRU
===================
The Unevictable LRU facility adds an additional LRU list to track unevictable
@@ -66,17 +42,17 @@ completely unresponsive.
The unevictable list addresses the following classes of unevictable pages:
- (*) Those owned by ramfs.
+ * Those owned by ramfs.
- (*) Those mapped into SHM_LOCK'd shared memory regions.
+ * Those mapped into SHM_LOCK'd shared memory regions.
- (*) Those mapped into VM_LOCKED [mlock()ed] VMAs.
+ * Those mapped into VM_LOCKED [mlock()ed] VMAs.
The infrastructure may also be able to handle other conditions that make pages
unevictable, either by definition or by circumstance, in the future.
-THE UNEVICTABLE PAGE LIST
+The Unevictable Page List
-------------------------
The Unevictable LRU infrastructure consists of an additional, per-zone, LRU list
@@ -118,7 +94,7 @@ the unevictable list when one task has the page isolated from the LRU and other
tasks are changing the "evictability" state of the page.
-MEMORY CONTROL GROUP INTERACTION
+Memory Control Group Interaction
--------------------------------
The unevictable LRU facility interacts with the memory control group [aka
@@ -144,7 +120,9 @@ effects:
the control group to thrash or to OOM-kill tasks.
-MARKING ADDRESS SPACES UNEVICTABLE
+.. _mark_addr_space_unevict:
+
+Marking Address Spaces Unevictable
----------------------------------
For facilities such as ramfs none of the pages attached to the address space
@@ -152,15 +130,15 @@ may be evicted. To prevent eviction of any such pages, the AS_UNEVICTABLE
address space flag is provided, and this can be manipulated by a filesystem
using a number of wrapper functions:
- (*) void mapping_set_unevictable(struct address_space *mapping);
+ * ``void mapping_set_unevictable(struct address_space *mapping);``
Mark the address space as being completely unevictable.
- (*) void mapping_clear_unevictable(struct address_space *mapping);
+ * ``void mapping_clear_unevictable(struct address_space *mapping);``
Mark the address space as being evictable.
- (*) int mapping_unevictable(struct address_space *mapping);
+ * ``int mapping_unevictable(struct address_space *mapping);``
Query the address space, and return true if it is completely
unevictable.
@@ -177,12 +155,13 @@ These are currently used in two places in the kernel:
ensure they're in memory.
-DETECTING UNEVICTABLE PAGES
+Detecting Unevictable Pages
---------------------------
The function page_evictable() in vmscan.c determines whether a page is
-evictable or not using the query function outlined above [see section "Marking
-address spaces unevictable"] to check the AS_UNEVICTABLE flag.
+evictable or not using the query function outlined above [see section
+:ref:`Marking address spaces unevictable <mark_addr_space_unevict>`]
+to check the AS_UNEVICTABLE flag.
For address spaces that are so marked after being populated (as SHM regions
might be), the lock action (eg: SHM_LOCK) can be lazy, and need not populate
@@ -202,7 +181,7 @@ flag, PG_mlocked (as wrapped by PageMlocked()), which is set when a page is
faulted into a VM_LOCKED vma, or found in a vma being VM_LOCKED.
-VMSCAN'S HANDLING OF UNEVICTABLE PAGES
+Vmscan's Handling of Unevictable Pages
--------------------------------------
If unevictable pages are culled in the fault path, or moved to the unevictable
@@ -233,8 +212,7 @@ extra evictabilty checks should not occur in the majority of calls to
putback_lru_page().
-=============
-MLOCKED PAGES
+MLOCKED Pages
=============
The unevictable page list is also useful for mlock(), in addition to ramfs and
@@ -242,7 +220,7 @@ SYSV SHM. Note that mlock() is only available in CONFIG_MMU=y situations; in
NOMMU situations, all mappings are effectively mlocked.
-HISTORY
+History
-------
The "Unevictable mlocked Pages" infrastructure is based on work originally
@@ -263,7 +241,7 @@ replaced by walking the reverse map to determine whether any VM_LOCKED VMAs
mapped the page. More on this below.
-BASIC MANAGEMENT
+Basic Management
----------------
mlocked pages - pages mapped into a VM_LOCKED VMA - are a class of unevictable
@@ -304,10 +282,10 @@ mlocked pages become unlocked and rescued from the unevictable list when:
(4) before a page is COW'd in a VM_LOCKED VMA.
-mlock()/mlockall() SYSTEM CALL HANDLING
+mlock()/mlockall() System Call Handling
---------------------------------------
-Both [do_]mlock() and [do_]mlockall() system call handlers call mlock_fixup()
+Both [do\_]mlock() and [do\_]mlockall() system call handlers call mlock_fixup()
for each VMA in the range specified by the call. In the case of mlockall(),
this is the entire active address space of the task. Note that mlock_fixup()
is used for both mlocking and munlocking a range of memory. A call to mlock()
@@ -351,7 +329,7 @@ mlock_vma_page() is unable to isolate the page from the LRU, vmscan will handle
it later if and when it attempts to reclaim the page.
-FILTERING SPECIAL VMAS
+Filtering Special VMAs
----------------------
mlock_fixup() filters several classes of "special" VMAs:
@@ -379,8 +357,9 @@ VM_LOCKED flag. Therefore, we won't have to deal with them later during
munlock(), munmap() or task exit. Neither does mlock_fixup() account these
VMAs against the task's "locked_vm".
+.. _munlock_munlockall_handling:
-munlock()/munlockall() SYSTEM CALL HANDLING
+munlock()/munlockall() System Call Handling
-------------------------------------------
The munlock() and munlockall() system calls are handled by the same functions -
@@ -426,7 +405,7 @@ This is fine, because we'll catch it later if and if vmscan tries to reclaim
the page. This should be relatively rare.
-MIGRATING MLOCKED PAGES
+Migrating MLOCKED Pages
-----------------------
A page that is being migrated has been isolated from the LRU lists and is held
@@ -451,7 +430,7 @@ list because of a race between munlock and migration, page migration uses the
putback_lru_page() function to add migrated pages back to the LRU.
-COMPACTING MLOCKED PAGES
+Compacting MLOCKED Pages
------------------------
The unevictable LRU can be scanned for compactable regions and the default
@@ -461,7 +440,7 @@ unevictable LRU is enabled, the work of compaction is mostly handled by
the page migration code and the same work flow as described in MIGRATING
MLOCKED PAGES will apply.
-MLOCKING TRANSPARENT HUGE PAGES
+MLOCKING Transparent Huge Pages
-------------------------------
A transparent huge page is represented by a single entry on an LRU list.
@@ -483,7 +462,7 @@ to unevictable LRU and the rest can be reclaimed.
See also comment in follow_trans_huge_pmd().
-mmap(MAP_LOCKED) SYSTEM CALL HANDLING
+mmap(MAP_LOCKED) System Call Handling
-------------------------------------
In addition the mlock()/mlockall() system calls, an application can request
@@ -514,7 +493,7 @@ memory range accounted as locked_vm, as the protections could be changed later
and pages allocated into that region.
-munmap()/exit()/exec() SYSTEM CALL HANDLING
+munmap()/exit()/exec() System Call Handling
-------------------------------------------
When unmapping an mlocked region of memory, whether by an explicit call to
@@ -568,16 +547,18 @@ munlock or munmap system calls, mm teardown (munlock_vma_pages_all), reclaim,
holepunching, and truncation of file pages and their anonymous COWed pages.
-try_to_munlock() REVERSE MAP SCAN
+try_to_munlock() Reverse Map Scan
---------------------------------
- [!] TODO/FIXME: a better name might be page_mlocked() - analogous to the
- page_referenced() reverse map walker.
+.. warning::
+ [!] TODO/FIXME: a better name might be page_mlocked() - analogous to the
+ page_referenced() reverse map walker.
-When munlock_vma_page() [see section "munlock()/munlockall() System Call
-Handling" above] tries to munlock a page, it needs to determine whether or not
-the page is mapped by any VM_LOCKED VMA without actually attempting to unmap
-all PTEs from the page. For this purpose, the unevictable/mlock infrastructure
+When munlock_vma_page() [see section :ref:`munlock()/munlockall() System Call
+Handling <munlock_munlockall_handling>` above] tries to munlock a
+page, it needs to determine whether or not the page is mapped by any
+VM_LOCKED VMA without actually attempting to unmap all PTEs from the
+page. For this purpose, the unevictable/mlock infrastructure
introduced a variant of try_to_unmap() called try_to_munlock().
try_to_munlock() calls the same functions as try_to_unmap() for anonymous and
@@ -595,7 +576,7 @@ large region or tearing down a large address space that has been mlocked via
mlockall(), overall this is a fairly rare event.
-PAGE RECLAIM IN shrink_*_list()
+Page Reclaim in shrink_*_list()
-------------------------------
shrink_active_list() culls any obviously unevictable pages - i.e.
--
2.7.4
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