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Date: Wed, 5 May 2021 15:08:27 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: dave.hansen@...el.com, luto@...nel.org, peterz@...radead.org,
linux-mm@...ck.org, x86@...nel.org, akpm@...ux-foundation.org,
linux-hardening@...r.kernel.org,
kernel-hardening@...ts.openwall.com, ira.weiny@...el.com,
dan.j.williams@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 3/9] x86/mm/cpa: Add grouped page allocations
On Tue, May 04, 2021 at 05:30:26PM -0700, Rick Edgecombe wrote:
> For x86, setting memory permissions on the direct map results in fracturing
> large pages. Direct map fracturing can be reduced by locating pages that
> will have their permissions set close together.
>
> Create a simple page cache that allocates pages from huge page size
> blocks. Don't guarantee that a page will come from a huge page grouping,
> instead fallback to non-grouped pages to fulfill the allocation if
> needed. Also, register a shrinker such that the system can ask for the
> pages back if needed. Since this is only needed when there is a direct
> map, compile it out on highmem systems.
I only had time to skim through the patches, I like the idea of having a
simple cache that allocates larger pages with a fallback to basic page
size.
I just think it should be more generic and closer to the page allocator.
I was thinking about adding a GFP flag that will tell that the allocated
pages should be removed from the direct map. Then alloc_pages() could use
such cache whenever this GFP flag is specified with a fallback for lower
order allocations.
> Free pages in the cache are kept track of in per-node list inside a
> list_lru. NUMA_NO_NODE requests are serviced by checking each per-node
> list in a round robin fashion. If pages are requested for a certain node
> but the cache is empty for that node, a whole additional huge page size
> page is allocated.
>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> ---
> arch/x86/include/asm/set_memory.h | 14 +++
> arch/x86/mm/pat/set_memory.c | 151 ++++++++++++++++++++++++++++++
> 2 files changed, 165 insertions(+)
>
> diff --git a/arch/x86/include/asm/set_memory.h b/arch/x86/include/asm/set_memory.h
> index 4352f08bfbb5..b63f09cc282a 100644
> --- a/arch/x86/include/asm/set_memory.h
> +++ b/arch/x86/include/asm/set_memory.h
> @@ -4,6 +4,9 @@
>
> #include <asm/page.h>
> #include <asm-generic/set_memory.h>
> +#include <linux/gfp.h>
> +#include <linux/list_lru.h>
> +#include <linux/shrinker.h>
>
> /*
> * The set_memory_* API can be used to change various attributes of a virtual
> @@ -135,4 +138,15 @@ static inline int clear_mce_nospec(unsigned long pfn)
> */
> #endif
>
> +struct grouped_page_cache {
> + struct shrinker shrinker;
> + struct list_lru lru;
> + gfp_t gfp;
> + atomic_t nid_round_robin;
> +};
> +
> +int init_grouped_page_cache(struct grouped_page_cache *gpc, gfp_t gfp);
> +struct page *get_grouped_page(int node, struct grouped_page_cache *gpc);
> +void free_grouped_page(struct grouped_page_cache *gpc, struct page *page);
> +
> #endif /* _ASM_X86_SET_MEMORY_H */
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index 16f878c26667..6877ef66793b 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -2306,6 +2306,157 @@ int __init kernel_unmap_pages_in_pgd(pgd_t *pgd, unsigned long address,
> return retval;
> }
>
> +#ifndef HIGHMEM
> +static struct page *__alloc_page_order(int node, gfp_t gfp_mask, int order)
> +{
> + if (node == NUMA_NO_NODE)
> + return alloc_pages(gfp_mask, order);
> +
> + return alloc_pages_node(node, gfp_mask, order);
> +}
> +
> +static struct grouped_page_cache *__get_gpc_from_sc(struct shrinker *shrinker)
> +{
> + return container_of(shrinker, struct grouped_page_cache, shrinker);
> +}
> +
> +static unsigned long grouped_shrink_count(struct shrinker *shrinker,
> + struct shrink_control *sc)
> +{
> + struct grouped_page_cache *gpc = __get_gpc_from_sc(shrinker);
> + unsigned long page_cnt = list_lru_shrink_count(&gpc->lru, sc);
> +
> + return page_cnt ? page_cnt : SHRINK_EMPTY;
> +}
> +
> +static enum lru_status grouped_isolate(struct list_head *item,
> + struct list_lru_one *list,
> + spinlock_t *lock, void *cb_arg)
> +{
> + struct list_head *dispose = cb_arg;
> +
> + list_lru_isolate_move(list, item, dispose);
> +
> + return LRU_REMOVED;
> +}
> +
> +static void __dispose_pages(struct grouped_page_cache *gpc, struct list_head *head)
> +{
> + struct list_head *cur, *next;
> +
> + list_for_each_safe(cur, next, head) {
> + struct page *page = list_entry(head, struct page, lru);
> +
> + list_del(cur);
> +
> + __free_pages(page, 0);
> + }
> +}
> +
> +static unsigned long grouped_shrink_scan(struct shrinker *shrinker,
> + struct shrink_control *sc)
> +{
> + struct grouped_page_cache *gpc = __get_gpc_from_sc(shrinker);
> + unsigned long isolated;
> + LIST_HEAD(freeable);
> +
> + if (!(sc->gfp_mask & gpc->gfp))
> + return SHRINK_STOP;
> +
> + isolated = list_lru_shrink_walk(&gpc->lru, sc, grouped_isolate,
> + &freeable);
> + __dispose_pages(gpc, &freeable);
> +
> + /* Every item walked gets isolated */
> + sc->nr_scanned += isolated;
> +
> + return isolated;
> +}
> +
> +static struct page *__remove_first_page(struct grouped_page_cache *gpc, int node)
> +{
> + unsigned int start_nid, i;
> + struct list_head *head;
> +
> + if (node != NUMA_NO_NODE) {
> + head = list_lru_get_mru(&gpc->lru, node);
> + if (head)
> + return list_entry(head, struct page, lru);
> + return NULL;
> + }
> +
> + /* If NUMA_NO_NODE, search the nodes in round robin for a page */
> + start_nid = (unsigned int)atomic_fetch_inc(&gpc->nid_round_robin) % nr_node_ids;
> + for (i = 0; i < nr_node_ids; i++) {
> + int cur_nid = (start_nid + i) % nr_node_ids;
> +
> + head = list_lru_get_mru(&gpc->lru, cur_nid);
> + if (head)
> + return list_entry(head, struct page, lru);
> + }
> +
> + return NULL;
> +}
> +
> +/* Get and add some new pages to the cache to be used by VM_GROUP_PAGES */
> +static struct page *__replenish_grouped_pages(struct grouped_page_cache *gpc, int node)
> +{
> + const unsigned int hpage_cnt = HPAGE_SIZE >> PAGE_SHIFT;
> + struct page *page;
> + int i;
> +
> + page = __alloc_page_order(node, gpc->gfp, HUGETLB_PAGE_ORDER);
> + if (!page)
> + return __alloc_page_order(node, gpc->gfp, 0);
> +
> + split_page(page, HUGETLB_PAGE_ORDER);
> +
> + for (i = 1; i < hpage_cnt; i++)
> + free_grouped_page(gpc, &page[i]);
> +
> + return &page[0];
> +}
> +
> +int init_grouped_page_cache(struct grouped_page_cache *gpc, gfp_t gfp)
> +{
> + int err = 0;
> +
> + memset(gpc, 0, sizeof(struct grouped_page_cache));
> +
> + if (list_lru_init(&gpc->lru))
> + goto out;
> +
> + gpc->shrinker.count_objects = grouped_shrink_count;
> + gpc->shrinker.scan_objects = grouped_shrink_scan;
> + gpc->shrinker.seeks = DEFAULT_SEEKS;
> + gpc->shrinker.flags = SHRINKER_NUMA_AWARE;
> +
> + err = register_shrinker(&gpc->shrinker);
> + if (err)
> + list_lru_destroy(&gpc->lru);
> +
> +out:
> + return err;
> +}
> +
> +struct page *get_grouped_page(int node, struct grouped_page_cache *gpc)
> +{
> + struct page *page;
> +
> + page = __remove_first_page(gpc, node);
> +
> + if (page)
> + return page;
> +
> + return __replenish_grouped_pages(gpc, node);
> +}
> +
> +void free_grouped_page(struct grouped_page_cache *gpc, struct page *page)
> +{
> + INIT_LIST_HEAD(&page->lru);
> + list_lru_add_node(&gpc->lru, &page->lru, page_to_nid(page));
> +}
> +#endif /* !HIGHMEM */
> /*
> * The testcases use internal knowledge of the implementation that shouldn't
> * be exposed to the rest of the kernel. Include these directly here.
> --
> 2.30.2
>
--
Sincerely yours,
Mike.
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