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![Vladimir Davydov](/assets/img/avatar_default.png)
Knowing the portion of memory that is not used by a certain application or memory cgroup (idle memory) can be useful for partitioning the system efficiently, e.g. by setting memory cgroup limits appropriately. Currently, the only means to estimate the amount of idle memory provided by the kernel is /proc/PID/{clear_refs,smaps}: the user can clear the access bit for all pages mapped to a particular process by writing 1 to clear_refs, wait for some time, and then count smaps:Referenced. However, this method has two serious shortcomings: - it does not count unmapped file pages - it affects the reclaimer logic To overcome these drawbacks, this patch introduces two new page flags, Idle and Young, and a new sysfs file, /sys/kernel/mm/page_idle/bitmap. A page's Idle flag can only be set from userspace by setting bit in /sys/kernel/mm/page_idle/bitmap at the offset corresponding to the page, and it is cleared whenever the page is accessed either through page tables (it is cleared in page_referenced() in this case) or using the read(2) system call (mark_page_accessed()). Thus by setting the Idle flag for pages of a particular workload, which can be found e.g. by reading /proc/PID/pagemap, waiting for some time to let the workload access its working set, and then reading the bitmap file, one can estimate the amount of pages that are not used by the workload. The Young page flag is used to avoid interference with the memory reclaimer. A page's Young flag is set whenever the Access bit of a page table entry pointing to the page is cleared by writing to the bitmap file. If page_referenced() is called on a Young page, it will add 1 to its return value, therefore concealing the fact that the Access bit was cleared. Note, since there is no room for extra page flags on 32 bit, this feature uses extended page flags when compiled on 32 bit. [akpm@linux-foundation.org: fix build] [akpm@linux-foundation.org: kpageidle requires an MMU] [akpm@linux-foundation.org: decouple from page-flags rework] Signed-off-by: Vladimir Davydov <vdavydov@parallels.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: Greg Thelen <gthelen@google.com> Cc: Michel Lespinasse <walken@google.com> Cc: David Rientjes <rientjes@google.com> Cc: Pavel Emelyanov <xemul@parallels.com> Cc: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
407 lines
10 KiB
C
407 lines
10 KiB
C
#include <linux/mm.h>
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#include <linux/mmzone.h>
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#include <linux/bootmem.h>
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#include <linux/page_ext.h>
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#include <linux/memory.h>
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#include <linux/vmalloc.h>
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#include <linux/kmemleak.h>
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#include <linux/page_owner.h>
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#include <linux/page_idle.h>
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/*
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* struct page extension
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*
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* This is the feature to manage memory for extended data per page.
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*
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* Until now, we must modify struct page itself to store extra data per page.
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* This requires rebuilding the kernel and it is really time consuming process.
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* And, sometimes, rebuild is impossible due to third party module dependency.
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* At last, enlarging struct page could cause un-wanted system behaviour change.
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*
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* This feature is intended to overcome above mentioned problems. This feature
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* allocates memory for extended data per page in certain place rather than
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* the struct page itself. This memory can be accessed by the accessor
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* functions provided by this code. During the boot process, it checks whether
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* allocation of huge chunk of memory is needed or not. If not, it avoids
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* allocating memory at all. With this advantage, we can include this feature
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* into the kernel in default and can avoid rebuild and solve related problems.
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*
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* To help these things to work well, there are two callbacks for clients. One
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* is the need callback which is mandatory if user wants to avoid useless
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* memory allocation at boot-time. The other is optional, init callback, which
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* is used to do proper initialization after memory is allocated.
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*
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* The need callback is used to decide whether extended memory allocation is
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* needed or not. Sometimes users want to deactivate some features in this
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* boot and extra memory would be unneccessary. In this case, to avoid
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* allocating huge chunk of memory, each clients represent their need of
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* extra memory through the need callback. If one of the need callbacks
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* returns true, it means that someone needs extra memory so that
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* page extension core should allocates memory for page extension. If
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* none of need callbacks return true, memory isn't needed at all in this boot
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* and page extension core can skip to allocate memory. As result,
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* none of memory is wasted.
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*
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* The init callback is used to do proper initialization after page extension
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* is completely initialized. In sparse memory system, extra memory is
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* allocated some time later than memmap is allocated. In other words, lifetime
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* of memory for page extension isn't same with memmap for struct page.
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* Therefore, clients can't store extra data until page extension is
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* initialized, even if pages are allocated and used freely. This could
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* cause inadequate state of extra data per page, so, to prevent it, client
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* can utilize this callback to initialize the state of it correctly.
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*/
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static struct page_ext_operations *page_ext_ops[] = {
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&debug_guardpage_ops,
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#ifdef CONFIG_PAGE_POISONING
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&page_poisoning_ops,
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#endif
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#ifdef CONFIG_PAGE_OWNER
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&page_owner_ops,
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#endif
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#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
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&page_idle_ops,
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#endif
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};
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static unsigned long total_usage;
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static bool __init invoke_need_callbacks(void)
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{
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int i;
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int entries = ARRAY_SIZE(page_ext_ops);
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for (i = 0; i < entries; i++) {
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if (page_ext_ops[i]->need && page_ext_ops[i]->need())
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return true;
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}
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return false;
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}
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static void __init invoke_init_callbacks(void)
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{
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int i;
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int entries = ARRAY_SIZE(page_ext_ops);
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for (i = 0; i < entries; i++) {
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if (page_ext_ops[i]->init)
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page_ext_ops[i]->init();
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}
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}
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#if !defined(CONFIG_SPARSEMEM)
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void __meminit pgdat_page_ext_init(struct pglist_data *pgdat)
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{
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pgdat->node_page_ext = NULL;
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}
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struct page_ext *lookup_page_ext(struct page *page)
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{
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unsigned long pfn = page_to_pfn(page);
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unsigned long offset;
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struct page_ext *base;
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base = NODE_DATA(page_to_nid(page))->node_page_ext;
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#ifdef CONFIG_DEBUG_VM
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/*
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* The sanity checks the page allocator does upon freeing a
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* page can reach here before the page_ext arrays are
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* allocated when feeding a range of pages to the allocator
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* for the first time during bootup or memory hotplug.
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*/
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if (unlikely(!base))
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return NULL;
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#endif
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offset = pfn - round_down(node_start_pfn(page_to_nid(page)),
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MAX_ORDER_NR_PAGES);
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return base + offset;
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}
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static int __init alloc_node_page_ext(int nid)
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{
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struct page_ext *base;
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unsigned long table_size;
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unsigned long nr_pages;
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nr_pages = NODE_DATA(nid)->node_spanned_pages;
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if (!nr_pages)
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return 0;
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/*
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* Need extra space if node range is not aligned with
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* MAX_ORDER_NR_PAGES. When page allocator's buddy algorithm
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* checks buddy's status, range could be out of exact node range.
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*/
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if (!IS_ALIGNED(node_start_pfn(nid), MAX_ORDER_NR_PAGES) ||
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!IS_ALIGNED(node_end_pfn(nid), MAX_ORDER_NR_PAGES))
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nr_pages += MAX_ORDER_NR_PAGES;
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table_size = sizeof(struct page_ext) * nr_pages;
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base = memblock_virt_alloc_try_nid_nopanic(
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table_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS),
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BOOTMEM_ALLOC_ACCESSIBLE, nid);
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if (!base)
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return -ENOMEM;
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NODE_DATA(nid)->node_page_ext = base;
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total_usage += table_size;
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return 0;
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}
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void __init page_ext_init_flatmem(void)
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{
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int nid, fail;
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if (!invoke_need_callbacks())
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return;
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for_each_online_node(nid) {
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fail = alloc_node_page_ext(nid);
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if (fail)
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goto fail;
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}
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pr_info("allocated %ld bytes of page_ext\n", total_usage);
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invoke_init_callbacks();
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return;
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fail:
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pr_crit("allocation of page_ext failed.\n");
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panic("Out of memory");
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}
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#else /* CONFIG_FLAT_NODE_MEM_MAP */
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struct page_ext *lookup_page_ext(struct page *page)
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{
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unsigned long pfn = page_to_pfn(page);
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struct mem_section *section = __pfn_to_section(pfn);
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#ifdef CONFIG_DEBUG_VM
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/*
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* The sanity checks the page allocator does upon freeing a
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* page can reach here before the page_ext arrays are
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* allocated when feeding a range of pages to the allocator
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* for the first time during bootup or memory hotplug.
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*/
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if (!section->page_ext)
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return NULL;
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#endif
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return section->page_ext + pfn;
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}
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static void *__meminit alloc_page_ext(size_t size, int nid)
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{
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gfp_t flags = GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN;
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void *addr = NULL;
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addr = alloc_pages_exact_nid(nid, size, flags);
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if (addr) {
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kmemleak_alloc(addr, size, 1, flags);
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return addr;
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}
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if (node_state(nid, N_HIGH_MEMORY))
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addr = vzalloc_node(size, nid);
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else
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addr = vzalloc(size);
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return addr;
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}
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static int __meminit init_section_page_ext(unsigned long pfn, int nid)
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{
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struct mem_section *section;
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struct page_ext *base;
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unsigned long table_size;
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section = __pfn_to_section(pfn);
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if (section->page_ext)
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return 0;
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table_size = sizeof(struct page_ext) * PAGES_PER_SECTION;
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base = alloc_page_ext(table_size, nid);
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/*
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* The value stored in section->page_ext is (base - pfn)
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* and it does not point to the memory block allocated above,
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* causing kmemleak false positives.
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*/
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kmemleak_not_leak(base);
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if (!base) {
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pr_err("page ext allocation failure\n");
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return -ENOMEM;
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}
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/*
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* The passed "pfn" may not be aligned to SECTION. For the calculation
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* we need to apply a mask.
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*/
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pfn &= PAGE_SECTION_MASK;
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section->page_ext = base - pfn;
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total_usage += table_size;
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return 0;
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}
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#ifdef CONFIG_MEMORY_HOTPLUG
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static void free_page_ext(void *addr)
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{
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if (is_vmalloc_addr(addr)) {
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vfree(addr);
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} else {
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struct page *page = virt_to_page(addr);
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size_t table_size;
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table_size = sizeof(struct page_ext) * PAGES_PER_SECTION;
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BUG_ON(PageReserved(page));
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free_pages_exact(addr, table_size);
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}
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}
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static void __free_page_ext(unsigned long pfn)
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{
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struct mem_section *ms;
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struct page_ext *base;
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ms = __pfn_to_section(pfn);
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if (!ms || !ms->page_ext)
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return;
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base = ms->page_ext + pfn;
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free_page_ext(base);
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ms->page_ext = NULL;
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}
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static int __meminit online_page_ext(unsigned long start_pfn,
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unsigned long nr_pages,
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int nid)
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{
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unsigned long start, end, pfn;
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int fail = 0;
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start = SECTION_ALIGN_DOWN(start_pfn);
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end = SECTION_ALIGN_UP(start_pfn + nr_pages);
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if (nid == -1) {
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/*
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* In this case, "nid" already exists and contains valid memory.
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* "start_pfn" passed to us is a pfn which is an arg for
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* online__pages(), and start_pfn should exist.
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*/
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nid = pfn_to_nid(start_pfn);
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VM_BUG_ON(!node_state(nid, N_ONLINE));
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}
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for (pfn = start; !fail && pfn < end; pfn += PAGES_PER_SECTION) {
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if (!pfn_present(pfn))
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continue;
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fail = init_section_page_ext(pfn, nid);
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}
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if (!fail)
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return 0;
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/* rollback */
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for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION)
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__free_page_ext(pfn);
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return -ENOMEM;
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}
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static int __meminit offline_page_ext(unsigned long start_pfn,
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unsigned long nr_pages, int nid)
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{
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unsigned long start, end, pfn;
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start = SECTION_ALIGN_DOWN(start_pfn);
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end = SECTION_ALIGN_UP(start_pfn + nr_pages);
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for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION)
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__free_page_ext(pfn);
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return 0;
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}
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static int __meminit page_ext_callback(struct notifier_block *self,
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unsigned long action, void *arg)
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{
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struct memory_notify *mn = arg;
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int ret = 0;
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switch (action) {
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case MEM_GOING_ONLINE:
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ret = online_page_ext(mn->start_pfn,
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mn->nr_pages, mn->status_change_nid);
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break;
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case MEM_OFFLINE:
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offline_page_ext(mn->start_pfn,
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mn->nr_pages, mn->status_change_nid);
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break;
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case MEM_CANCEL_ONLINE:
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offline_page_ext(mn->start_pfn,
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mn->nr_pages, mn->status_change_nid);
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break;
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case MEM_GOING_OFFLINE:
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break;
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case MEM_ONLINE:
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case MEM_CANCEL_OFFLINE:
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break;
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}
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return notifier_from_errno(ret);
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}
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#endif
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void __init page_ext_init(void)
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{
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unsigned long pfn;
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int nid;
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if (!invoke_need_callbacks())
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return;
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for_each_node_state(nid, N_MEMORY) {
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unsigned long start_pfn, end_pfn;
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start_pfn = node_start_pfn(nid);
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end_pfn = node_end_pfn(nid);
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/*
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* start_pfn and end_pfn may not be aligned to SECTION and the
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* page->flags of out of node pages are not initialized. So we
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* scan [start_pfn, the biggest section's pfn < end_pfn) here.
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*/
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for (pfn = start_pfn; pfn < end_pfn;
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pfn = ALIGN(pfn + 1, PAGES_PER_SECTION)) {
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if (!pfn_valid(pfn))
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continue;
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/*
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* Nodes's pfns can be overlapping.
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* We know some arch can have a nodes layout such as
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* -------------pfn-------------->
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* N0 | N1 | N2 | N0 | N1 | N2|....
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*/
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if (pfn_to_nid(pfn) != nid)
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continue;
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if (init_section_page_ext(pfn, nid))
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goto oom;
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}
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}
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hotplug_memory_notifier(page_ext_callback, 0);
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pr_info("allocated %ld bytes of page_ext\n", total_usage);
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invoke_init_callbacks();
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return;
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oom:
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panic("Out of memory");
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}
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void __meminit pgdat_page_ext_init(struct pglist_data *pgdat)
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{
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}
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#endif
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