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Diffstat (limited to 'Documentation/filesystems/proc.rst')
| -rw-r--r-- | Documentation/filesystems/proc.rst | 53 |
1 files changed, 48 insertions, 5 deletions
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 09f0aed5a08b..2a17865dfe39 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -128,6 +128,16 @@ process running on the system, which is named after the process ID (PID). The link 'self' points to the process reading the file system. Each process subdirectory has the entries listed in Table 1-1. +A process can read its own information from /proc/PID/* with no extra +permissions. When reading /proc/PID/* information for other processes, reading +process is required to have either CAP_SYS_PTRACE capability with +PTRACE_MODE_READ access permissions, or, alternatively, CAP_PERFMON +capability. This applies to all read-only information like `maps`, `environ`, +`pagemap`, etc. The only exception is `mem` file due to its read-write nature, +which requires CAP_SYS_PTRACE capabilities with more elevated +PTRACE_MODE_ATTACH permissions; CAP_PERFMON capability does not grant access +to /proc/PID/mem for other processes. + Note that an open file descriptor to /proc/<pid> or to any of its contained files or subdirectories does not prevent <pid> being reused for some other process in the event that <pid> exits. Operations on @@ -502,9 +512,25 @@ process, its PSS will be 1500. "Pss_Dirty" is the portion of PSS which consists of dirty pages. ("Pss_Clean" is not included, but it can be calculated by subtracting "Pss_Dirty" from "Pss".) -Note that even a page which is part of a MAP_SHARED mapping, but has only -a single pte mapped, i.e. is currently used by only one process, is accounted -as private and not as shared. +Traditionally, a page is accounted as "private" if it is mapped exactly once, +and a page is accounted as "shared" when mapped multiple times, even when +mapped in the same process multiple times. Note that this accounting is +independent of MAP_SHARED. + +In some kernel configurations, the semantics of pages part of a larger +allocation (e.g., THP) can differ: a page is accounted as "private" if all +pages part of the corresponding large allocation are *certainly* mapped in the +same process, even if the page is mapped multiple times in that process. A +page is accounted as "shared" if any page page of the larger allocation +is *maybe* mapped in a different process. In some cases, a large allocation +might be treated as "maybe mapped by multiple processes" even though this +is no longer the case. + +Some kernel configurations do not track the precise number of times a page part +of a larger allocation is mapped. In this case, when calculating the PSS, the +average number of mappings per page in this larger allocation might be used +as an approximation for the number of mappings of a page. The PSS calculation +will be imprecise in this case. "Referenced" indicates the amount of memory currently marked as referenced or accessed. @@ -686,6 +712,11 @@ Where: node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page size, in KB, that is backing the mapping up. +Note that some kernel configurations do not track the precise number of times +a page part of a larger allocation (e.g., THP) is mapped. In these +configurations, "mapmax" might corresponds to the average number of mappings +per page in such a larger allocation instead. + 1.2 Kernel data --------------- @@ -1060,6 +1091,8 @@ Example output. You may not have all of these fields. FilePmdMapped: 0 kB CmaTotal: 0 kB CmaFree: 0 kB + Unaccepted: 0 kB + Balloon: 0 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 @@ -1132,9 +1165,15 @@ Dirty Writeback Memory which is actively being written back to the disk AnonPages - Non-file backed pages mapped into userspace page tables + Non-file backed pages mapped into userspace page tables. Note that + some kernel configurations might consider all pages part of a + larger allocation (e.g., THP) as "mapped", as soon as a single + page is mapped. Mapped - files which have been mmapped, such as libraries + files which have been mmapped, such as libraries. Note that some + kernel configurations might consider all pages part of a larger + allocation (e.g., THP) as "mapped", as soon as a single page is + mapped. Shmem Total memory used by shared memory (shmem) and tmpfs KReclaimable @@ -1228,6 +1267,10 @@ CmaTotal Memory reserved for the Contiguous Memory Allocator (CMA) CmaFree Free remaining memory in the CMA reserves +Unaccepted + Memory that has not been accepted by the guest +Balloon + Memory returned to Host by VM Balloon Drivers HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb See Documentation/admin-guide/mm/hugetlbpage.rst. DirectMap4k, DirectMap2M, DirectMap1G |