Merge tag 'docs-5.9' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "It's been a busy cycle for documentation - hopefully the busiest for a
  while to come. Changes include:

   - Some new Chinese translations

   - Progress on the battle against double words words and non-HTTPS
     URLs

   - Some block-mq documentation

   - More RST conversions from Mauro. At this point, that task is
     essentially complete, so we shouldn't see this kind of churn again
     for a while. Unless we decide to switch to asciidoc or
     something...:)

   - Lots of typo fixes, warning fixes, and more"

* tag 'docs-5.9' of git://git.lwn.net/linux: (195 commits)
  scripts/kernel-doc: optionally treat warnings as errors
  docs: ia64: correct typo
  mailmap: add entry for <alobakin@marvell.com>
  doc/zh_CN: add cpu-load Chinese version
  Documentation/admin-guide: tainted-kernels: fix spelling mistake
  MAINTAINERS: adjust kprobes.rst entry to new location
  devices.txt: document rfkill allocation
  PCI: correct flag name
  docs: filesystems: vfs: correct flag name
  docs: filesystems: vfs: correct sync_mode flag names
  docs: path-lookup: markup fixes for emphasis
  docs: path-lookup: more markup fixes
  docs: path-lookup: fix HTML entity mojibake
  CREDITS: Replace HTTP links with HTTPS ones
  docs: process: Add an example for creating a fixes tag
  doc/zh_CN: add Chinese translation prefer section
  doc/zh_CN: add clearing-warn-once Chinese version
  doc/zh_CN: add admin-guide index
  doc:it_IT: process: coding-style.rst: Correct __maybe_unused compiler label
  futex: MAINTAINERS: Re-add selftests directory
  ...

1 files changed, 44 insertions, 0 deletions

diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
index 4aa82ddd01b8..4446a1ac36cc 100644
--- a/Documentation/core-api/memory-allocation.rst
+++ b/Documentation/core-api/memory-allocation.rst
@@ -84,6 +84,50 @@ driver for a device with such restrictions, avoid using these flags.
 And even with hardware with restrictions it is preferable to use
 `dma_alloc*` APIs.
 
+GFP flags and reclaim behavior
+------------------------------
+Memory allocations may trigger direct or background reclaim and it is
+useful to understand how hard the page allocator will try to satisfy that
+or another request.
+
+  * ``GFP_KERNEL & ~__GFP_RECLAIM`` - optimistic allocation without _any_
+    attempt to free memory at all. The most light weight mode which even
+    doesn't kick the background reclaim. Should be used carefully because it
+    might deplete the memory and the next user might hit the more aggressive
+    reclaim.
+
+  * ``GFP_KERNEL & ~__GFP_DIRECT_RECLAIM`` (or ``GFP_NOWAIT``)- optimistic
+    allocation without any attempt to free memory from the current
+    context but can wake kswapd to reclaim memory if the zone is below
+    the low watermark. Can be used from either atomic contexts or when
+    the request is a performance optimization and there is another
+    fallback for a slow path.
+
+  * ``(GFP_KERNEL|__GFP_HIGH) & ~__GFP_DIRECT_RECLAIM`` (aka ``GFP_ATOMIC``) -
+    non sleeping allocation with an expensive fallback so it can access
+    some portion of memory reserves. Usually used from interrupt/bottom-half
+    context with an expensive slow path fallback.
+
+  * ``GFP_KERNEL`` - both background and direct reclaim are allowed and the
+    **default** page allocator behavior is used. That means that not costly
+    allocation requests are basically no-fail but there is no guarantee of
+    that behavior so failures have to be checked properly by callers
+    (e.g. OOM killer victim is allowed to fail currently).
+
+  * ``GFP_KERNEL | __GFP_NORETRY`` - overrides the default allocator behavior
+    and all allocation requests fail early rather than cause disruptive
+    reclaim (one round of reclaim in this implementation). The OOM killer
+    is not invoked.
+
+  * ``GFP_KERNEL | __GFP_RETRY_MAYFAIL`` - overrides the default allocator
+    behavior and all allocation requests try really hard. The request
+    will fail if the reclaim cannot make any progress. The OOM killer
+    won't be triggered.
+
+  * ``GFP_KERNEL | __GFP_NOFAIL`` - overrides the default allocator behavior
+    and all allocation requests will loop endlessly until they succeed.
+    This might be really dangerous especially for larger orders.
+
 Selecting memory allocator
 ==========================