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mm,page_alloc,cma: introduce a customisable threshold for allocating pages in cma

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On some platforms the cma area can be half the entire system memory,
meaning that allocations start happening in the cma area immediately.
This leads to fragmentation and subsequent fatal cma_alloc failures.

We introduce an "alloc_in_cma_threshold" parameter which requires that
this many sixteenths of the free pages must be in cma before it will
try to use them. By default this is set to 12, but the previous
behaviour can be restored by setting it to 8 on startup.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
This commit is contained in:
David Plowman
2022-03-29 16:10:06 +01:00
committed by Dom Cobley
parent 8eeafb2a0a
commit e8bd4fc1d6
1 changed files with 25 additions and 3 deletions
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28
mm/page_alloc.c
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@@ -207,6 +207,27 @@ EXPORT_SYMBOL(node_states);
gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
#define ALLOC_IN_CMA_THRESHOLD_MAX 16
#define ALLOC_IN_CMA_THRESHOLD_DEFAULT 12
static unsigned long _alloc_in_cma_threshold __read_mostly
= ALLOC_IN_CMA_THRESHOLD_DEFAULT;
static int __init alloc_in_cma_threshold_setup(char *buf)
{
unsigned long res;
if (kstrtoul(buf, 10, &res) < 0 ||
res > ALLOC_IN_CMA_THRESHOLD_MAX) {
pr_err("Bad alloc_cma_threshold value\n");
return 0;
}
_alloc_in_cma_threshold = res;
pr_info("Setting alloc_in_cma_threshold to %lu\n", res);
return 0;
}
early_param("alloc_in_cma_threshold", alloc_in_cma_threshold_setup);
#ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
unsigned int pageblock_order __read_mostly;
#endif
@@ -2245,12 +2266,13 @@ __rmqueue(struct zone *zone, unsigned int order, int migratetype,
if (IS_ENABLED(CONFIG_CMA)) {
/*
* Balance movable allocations between regular and CMA areas by
* allocating from CMA when over half of the zone's free memory
* is in the CMA area.
* allocating from CMA when over more than a given proportion of
* the zone's free memory is in the CMA area.
*/
if (alloc_flags & ALLOC_CMA &&
zone_page_state(zone, NR_FREE_CMA_PAGES) >
zone_page_state(zone, NR_FREE_PAGES) / 2) {
zone_page_state(zone, NR_FREE_PAGES) / ALLOC_IN_CMA_THRESHOLD_MAX
* _alloc_in_cma_threshold) {
page = __rmqueue_cma_fallback(zone, order);
if (page)
return page;