This will be similar to /sys/kernel/mm/page_idle/bitmap documented in Documentation/admin-guide/mm/idle_page_tracking.rst, however indexed by process virtual address.
When using the global PFN indexed idle bitmap, we find 2 kind of overheads: - to track a task's working set, Brendan Gregg end up writing wss-v1 for small tasks and wss-v2 for large tasks: https://github.com/brendangregg/wss That's because VAs may point to random PAs throughout the physical address space. So we either query /proc/pid/pagemap first and access the lots of random PFNs (with lots of syscalls) in the bitmap, or write+read the whole system idle bitmap beforehand. - page table walking by PFN has much more overheads than to walk a page table in its natural order: - rmap queries - more locking - random memory reads/writes This interface provides a cheap path for the majority non-shared mapping pages. To walk 1TB memory of 4k active pages, it costs 2s vs 15s system time to scan the per-task/global idle bitmaps. Which means ~7x speedup. The gap will be enlarged if consider - the extra /proc/pid/pagemap walk - natural page table walks can skip the whole 512 PTEs if PMD is idle OTOH, the per-task idle bitmap is not suitable in some situations: - not accurate for shared pages - don't work with non-mapped file pages - don't perform well for sparse page tables (pointed out by Huang Ying) So it's more about complementing the existing global idle bitmap. CC: Huang Ying <ying.hu...@intel.com> CC: Brendan Gregg <bgr...@netflix.com> Signed-off-by: Fengguang Wu <fengguang...@intel.com> --- fs/proc/base.c | 2 + fs/proc/internal.h | 1 fs/proc/task_mmu.c | 54 +++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 57 insertions(+) --- linux.orig/fs/proc/base.c 2018-12-23 20:08:14.228919325 +0800 +++ linux/fs/proc/base.c 2018-12-23 20:08:14.224919327 +0800 @@ -2969,6 +2969,7 @@ static const struct pid_entry tgid_base_ REG("smaps", S_IRUGO, proc_pid_smaps_operations), REG("smaps_rollup", S_IRUGO, proc_pid_smaps_rollup_operations), REG("pagemap", S_IRUSR, proc_pagemap_operations), + REG("idle_pages", S_IRUSR|S_IWUSR, proc_mm_idle_operations), #endif #ifdef CONFIG_SECURITY DIR("attr", S_IRUGO|S_IXUGO, proc_attr_dir_inode_operations, proc_attr_dir_operations), @@ -3357,6 +3358,7 @@ static const struct pid_entry tid_base_s REG("smaps", S_IRUGO, proc_pid_smaps_operations), REG("smaps_rollup", S_IRUGO, proc_pid_smaps_rollup_operations), REG("pagemap", S_IRUSR, proc_pagemap_operations), + REG("idle_pages", S_IRUSR|S_IWUSR, proc_mm_idle_operations), #endif #ifdef CONFIG_SECURITY DIR("attr", S_IRUGO|S_IXUGO, proc_attr_dir_inode_operations, proc_attr_dir_operations), --- linux.orig/fs/proc/internal.h 2018-12-23 20:08:14.228919325 +0800 +++ linux/fs/proc/internal.h 2018-12-23 20:08:14.224919327 +0800 @@ -298,6 +298,7 @@ extern const struct file_operations proc extern const struct file_operations proc_pid_smaps_rollup_operations; extern const struct file_operations proc_clear_refs_operations; extern const struct file_operations proc_pagemap_operations; +extern const struct file_operations proc_mm_idle_operations; extern unsigned long task_vsize(struct mm_struct *); extern unsigned long task_statm(struct mm_struct *, --- linux.orig/fs/proc/task_mmu.c 2018-12-23 20:08:14.228919325 +0800 +++ linux/fs/proc/task_mmu.c 2018-12-23 20:08:14.224919327 +0800 @@ -1559,6 +1559,60 @@ const struct file_operations proc_pagema .open = pagemap_open, .release = pagemap_release, }; + +/* will be filled when kvm_ept_idle module loads */ +struct file_operations proc_ept_idle_operations = { +}; +EXPORT_SYMBOL_GPL(proc_ept_idle_operations); + +static ssize_t mm_idle_read(struct file *file, char __user *buf, + size_t count, loff_t *ppos) +{ + if (proc_ept_idle_operations.read) + return proc_ept_idle_operations.read(file, buf, count, ppos); + + return 0; +} + + +static int mm_idle_open(struct inode *inode, struct file *file) +{ + struct mm_struct *mm = proc_mem_open(inode, PTRACE_MODE_READ); + + if (IS_ERR(mm)) + return PTR_ERR(mm); + + file->private_data = mm; + + if (proc_ept_idle_operations.open) + return proc_ept_idle_operations.open(inode, file); + + return 0; +} + +static int mm_idle_release(struct inode *inode, struct file *file) +{ + struct mm_struct *mm = file->private_data; + + if (mm) { + if (!mm_kvm(mm)) + flush_tlb_mm(mm); + mmdrop(mm); + } + + if (proc_ept_idle_operations.release) + return proc_ept_idle_operations.release(inode, file); + + return 0; +} + +const struct file_operations proc_mm_idle_operations = { + .llseek = mem_lseek, /* borrow this */ + .read = mm_idle_read, + .open = mm_idle_open, + .release = mm_idle_release, +}; + #endif /* CONFIG_PROC_PAGE_MONITOR */ #ifdef CONFIG_NUMA
