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mm/page_alloc: Separate THP PCP into movable and non-movable categories

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Since commit 5d0a661d80 ("mm/page_alloc: use only one PCP list for
THP-sized allocations") no longer differentiates the migration type of
pages in THP-sized PCP list, it's possible that non-movable allocation
requests may get a CMA page from the list, in some cases, it's not
acceptable.

If a large number of CMA memory are configured in system (for example, the
CMA memory accounts for 50% of the system memory), starting a virtual
machine with device passthrough will get stuck.  During starting the
virtual machine, it will call pin_user_pages_remote(..., FOLL_LONGTERM,
...) to pin memory.  Normally if a page is present and in CMA area,
pin_user_pages_remote() will migrate the page from CMA area to non-CMA
area because of FOLL_LONGTERM flag.  But if non-movable allocation
requests return CMA memory, migrate_longterm_unpinnable_pages() will
migrate a CMA page to another CMA page, which will fail to pass the check
in check_and_migrate_movable_pages() and cause migration endless.

Call trace:
pin_user_pages_remote
--__gup_longterm_locked // endless loops in this function
----_get_user_pages_locked
----check_and_migrate_movable_pages
------migrate_longterm_unpinnable_pages
--------alloc_migration_target

This problem will also have a negative impact on CMA itself.  For example,
when CMA is borrowed by THP, and we need to reclaim it through cma_alloc()
or dma_alloc_coherent(), we must move those pages out to ensure CMA's
users can retrieve that contigous memory.  Currently, CMA's memory is
occupied by non-movable pages, meaning we can't relocate them.  As a
result, cma_alloc() is more likely to fail.

To fix the problem above, we add one PCP list for THP, which will not
introduce a new cacheline for struct per_cpu_pages.  THP will have 2 PCP
lists, one PCP list is used by MOVABLE allocation, and the other PCP list
is used by UNMOVABLE allocation.  MOVABLE allocation contains GPF_MOVABLE,
and UNMOVABLE allocation contains GFP_UNMOVABLE and GFP_RECLAIMABLE.

Link: https://lkml.kernel.org/r/1718845190-4456-1-git-send-email-yangge1116@126.com
Fixes: 5d0a661d80 ("mm/page_alloc: use only one PCP list for THP-sized allocations")
Signed-off-by: yangge <yangge1116@126.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <21cnbao@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
yangge 2024-06-20 08:59:50 +08:00 committed by Andrew Morton
parent 54e7d59841
commit bf14ed81f5
2 changed files with 11 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
include/linux/mmzone.h
View File

@ -654,13 +654,12 @@ enum zone_watermarks {
};
/*
* One per migratetype for each PAGE_ALLOC_COSTLY_ORDER. One additional list
* for THP which will usually be GFP_MOVABLE. Even if it is another type,
* it should not contribute to serious fragmentation causing THP allocation
* failures.
* One per migratetype for each PAGE_ALLOC_COSTLY_ORDER. Two additional lists
* are added for THP. One PCP list is used by GPF_MOVABLE, and the other PCP list
* is used by GFP_UNMOVABLE and GFP_RECLAIMABLE.
*/
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
#define NR_PCP_THP 1
#define NR_PCP_THP 2
#else
#define NR_PCP_THP 0
#endif

9
mm/page_alloc.c
View File

@ -504,10 +504,15 @@ out:
static inline unsigned int order_to_pindex(int migratetype, int order)
{
bool __maybe_unused movable;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
if (order > PAGE_ALLOC_COSTLY_ORDER) {
VM_BUG_ON(order != HPAGE_PMD_ORDER);
return NR_LOWORDER_PCP_LISTS;
movable = migratetype == MIGRATE_MOVABLE;
return NR_LOWORDER_PCP_LISTS + movable;
}
#else
VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
@ -521,7 +526,7 @@ static inline int pindex_to_order(unsigned int pindex)
int order = pindex / MIGRATE_PCPTYPES;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
if (pindex == NR_LOWORDER_PCP_LISTS)
if (pindex >= NR_LOWORDER_PCP_LISTS)
order = HPAGE_PMD_ORDER;
#else
VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);