Hi all,
This patchset moves MIGRATE_ISOLATE to a standalone bit to avoid
being overwritten during pageblock isolation process. Currently,
MIGRATE_ISOLATE is part of enum migratetype (in include/linux/mmzone.h),
thus, setting a pageblock to MIGRATE_ISOLATE overwrites its original
migratetype. This causes pageblock migratetype loss during
alloc_contig_range() and memory offline, especially when the process
fails due to a failed pageblock isolation and the code tries to undo the
finished pageblock isolations.
I am also trying to collect feedback on how to handle MIGRATE_ISOLATE in
existing code. As MIGRATE_ISOLATE becomes a standalone bit like
PB_migrate_skip (pageblock skipped by compaction), in theory, existing code
could be changed to use {get,clear,set}_pageblock_isolate() like
{get,clear,set}_pageblock_skip() and MIGRATE_ISOLATE could be removed
from enum migratetype. But free list has a separate MIGRATE_ISOLATE list
and the memory info code used by OOM also shows free memory with
different migratetypes. I wonder if we want more extensive changes to
existing code to remove MIGRATE_ISOLATE. If not, what can I do to improve
the MIGRATE_ISOLATE specialized code in Patch 1? For example:
void set_pageblock_migratetype(struct page *page, int migratetype)
{
if (unlikely(page_group_by_mobility_disabled &&
migratetype < MIGRATE_PCPTYPES))
migratetype = MIGRATE_UNMOVABLE;
#ifdef CONFIG_MEMORY_ISOLATION
if (migratetype == MIGRATE_ISOLATE)
set_pageblock_isolate(page);
else
#endif
{
if (get_pageblock_isolate(page))
clear_pageblock_isolate(page);
set_pfnblock_flags_mask(page, (unsigned long)migratetype,
page_to_pfn(page), MIGRATETYPE_MASK);
}
}
Design
===
Pageblock flags are read in words to achieve good performance and existing
pageblock flags take 4 bits per pageblock. To avoid a substantial change
to the pageblock flag code, pageblock flag bits are expanded to use 8
and MIGRATE_ISOLATE is moved to use the last bit (bit 7).
It might look like the pageblock flags have doubled the overhead, but in
reality, the overhead is only 1 byte per 2MB/4MB (based on pageblock config),
or 0.0000476 %.
In terms of performance for changing pageblock types, I did a very
simple test by offlining and onlining all memory of a 16GB VM 10 times
and did not see a noticeable runtime difference with the patchset.
TODOs
===
1. improve pageblock migratetype handling code to be less hacky (see the
example above).
2. more performance tests on pageblock migratetype change.
Any comment and/or suggestion is welcome. Thanks.
Zi Yan (4):
mm/page_isolation: make page isolation a standalone bit.
mm/page_isolation: remove migratetype from
move_freepages_block_isolate()
mm/page_isolation: remove migratetype from undo_isolate_page_range()
mm/page_isolation: remove migratetype parameter from more functions.
include/linux/mmzone.h | 24 +++++++++++---
include/linux/page-isolation.h | 11 +++----
include/linux/pageblock-flags.h | 29 ++++++++++++++++-
mm/memory_hotplug.c | 5 ++-
mm/page_alloc.c | 55 +++++++++++++++++++++++++++------
mm/page_isolation.c | 55 ++++++++++++++-------------------
6 files changed, 123 insertions(+), 56 deletions(-)
--
2.45.2
