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![Randy Dunlap](/assets/img/avatar_default.png)
Fix stray kernel-doc warnings in mm/ due to mis-typed or missing function names. Quietens these kernel-doc warnings: mm/mmu_gather.c:264: warning: expecting prototype for tlb_gather_mmu(). Prototype was for __tlb_gather_mmu() instead mm/oom_kill.c:180: warning: expecting prototype for Check whether unreclaimable slab amount is greater than(). Prototype was for should_dump_unreclaim_slab() instead mm/shuffle.c:155: warning: expecting prototype for shuffle_free_memory(). Prototype was for __shuffle_free_memory() instead Link: https://lkml.kernel.org/r/20210411210642.11362-1-rdunlap@infradead.org Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
183 lines
4.7 KiB
C
183 lines
4.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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// Copyright(c) 2018 Intel Corporation. All rights reserved.
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#include <linux/mm.h>
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#include <linux/init.h>
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#include <linux/mmzone.h>
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#include <linux/random.h>
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#include <linux/moduleparam.h>
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#include "internal.h"
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#include "shuffle.h"
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DEFINE_STATIC_KEY_FALSE(page_alloc_shuffle_key);
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static bool shuffle_param;
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static int shuffle_show(char *buffer, const struct kernel_param *kp)
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{
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return sprintf(buffer, "%c\n", shuffle_param ? 'Y' : 'N');
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}
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static __meminit int shuffle_store(const char *val,
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const struct kernel_param *kp)
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{
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int rc = param_set_bool(val, kp);
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if (rc < 0)
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return rc;
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if (shuffle_param)
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static_branch_enable(&page_alloc_shuffle_key);
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return 0;
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}
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module_param_call(shuffle, shuffle_store, shuffle_show, &shuffle_param, 0400);
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/*
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* For two pages to be swapped in the shuffle, they must be free (on a
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* 'free_area' lru), have the same order, and have the same migratetype.
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*/
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static struct page * __meminit shuffle_valid_page(struct zone *zone,
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unsigned long pfn, int order)
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{
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struct page *page = pfn_to_online_page(pfn);
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/*
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* Given we're dealing with randomly selected pfns in a zone we
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* need to ask questions like...
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*/
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/* ... is the page managed by the buddy? */
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if (!page)
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return NULL;
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/* ... is the page assigned to the same zone? */
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if (page_zone(page) != zone)
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return NULL;
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/* ...is the page free and currently on a free_area list? */
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if (!PageBuddy(page))
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return NULL;
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/*
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* ...is the page on the same list as the page we will
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* shuffle it with?
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*/
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if (buddy_order(page) != order)
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return NULL;
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return page;
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}
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/*
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* Fisher-Yates shuffle the freelist which prescribes iterating through an
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* array, pfns in this case, and randomly swapping each entry with another in
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* the span, end_pfn - start_pfn.
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*
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* To keep the implementation simple it does not attempt to correct for sources
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* of bias in the distribution, like modulo bias or pseudo-random number
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* generator bias. I.e. the expectation is that this shuffling raises the bar
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* for attacks that exploit the predictability of page allocations, but need not
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* be a perfect shuffle.
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*/
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#define SHUFFLE_RETRY 10
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void __meminit __shuffle_zone(struct zone *z)
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{
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unsigned long i, flags;
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unsigned long start_pfn = z->zone_start_pfn;
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unsigned long end_pfn = zone_end_pfn(z);
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const int order = SHUFFLE_ORDER;
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const int order_pages = 1 << order;
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spin_lock_irqsave(&z->lock, flags);
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start_pfn = ALIGN(start_pfn, order_pages);
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for (i = start_pfn; i < end_pfn; i += order_pages) {
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unsigned long j;
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int migratetype, retry;
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struct page *page_i, *page_j;
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/*
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* We expect page_i, in the sub-range of a zone being added
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* (@start_pfn to @end_pfn), to more likely be valid compared to
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* page_j randomly selected in the span @zone_start_pfn to
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* @spanned_pages.
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*/
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page_i = shuffle_valid_page(z, i, order);
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if (!page_i)
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continue;
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for (retry = 0; retry < SHUFFLE_RETRY; retry++) {
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/*
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* Pick a random order aligned page in the zone span as
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* a swap target. If the selected pfn is a hole, retry
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* up to SHUFFLE_RETRY attempts find a random valid pfn
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* in the zone.
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*/
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j = z->zone_start_pfn +
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ALIGN_DOWN(get_random_long() % z->spanned_pages,
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order_pages);
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page_j = shuffle_valid_page(z, j, order);
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if (page_j && page_j != page_i)
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break;
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}
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if (retry >= SHUFFLE_RETRY) {
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pr_debug("%s: failed to swap %#lx\n", __func__, i);
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continue;
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}
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/*
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* Each migratetype corresponds to its own list, make sure the
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* types match otherwise we're moving pages to lists where they
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* do not belong.
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*/
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migratetype = get_pageblock_migratetype(page_i);
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if (get_pageblock_migratetype(page_j) != migratetype) {
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pr_debug("%s: migratetype mismatch %#lx\n", __func__, i);
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continue;
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}
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list_swap(&page_i->lru, &page_j->lru);
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pr_debug("%s: swap: %#lx -> %#lx\n", __func__, i, j);
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/* take it easy on the zone lock */
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if ((i % (100 * order_pages)) == 0) {
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spin_unlock_irqrestore(&z->lock, flags);
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cond_resched();
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spin_lock_irqsave(&z->lock, flags);
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}
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}
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spin_unlock_irqrestore(&z->lock, flags);
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}
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/*
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* __shuffle_free_memory - reduce the predictability of the page allocator
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* @pgdat: node page data
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*/
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void __meminit __shuffle_free_memory(pg_data_t *pgdat)
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{
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struct zone *z;
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for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
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shuffle_zone(z);
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}
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bool shuffle_pick_tail(void)
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{
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static u64 rand;
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static u8 rand_bits;
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bool ret;
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/*
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* The lack of locking is deliberate. If 2 threads race to
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* update the rand state it just adds to the entropy.
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*/
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if (rand_bits == 0) {
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rand_bits = 64;
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rand = get_random_u64();
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}
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ret = rand & 1;
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rand_bits--;
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rand >>= 1;
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return ret;
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}
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