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Diffstat (limited to 'Documentation/admin-guide/mm/transhuge.rst')
| -rw-r--r-- | Documentation/admin-guide/mm/transhuge.rst | 45 |
1 files changed, 20 insertions, 25 deletions
diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index 2f31de8f7c74..b0cc8243e093 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -1,5 +1,3 @@ -.. _admin_guide_transhuge: - ============================ Transparent Hugepage Support ============================ @@ -191,7 +189,14 @@ allocation failure to throttle the next allocation attempt:: /sys/kernel/mm/transparent_hugepage/khugepaged/alloc_sleep_millisecs -The khugepaged progress can be seen in the number of pages collapsed:: +The khugepaged progress can be seen in the number of pages collapsed (note +that this counter may not be an exact count of the number of pages +collapsed, since "collapsed" could mean multiple things: (1) A PTE mapping +being replaced by a PMD mapping, or (2) All 4K physical pages replaced by +one 2M hugepage. Each may happen independently, or together, depending on +the type of memory and the failures that occur. As such, this value should +be interpreted roughly as a sign of progress, and counters in /proc/vmstat +consulted for more accurate accounting):: /sys/kernel/mm/transparent_hugepage/khugepaged/pages_collapsed @@ -220,6 +225,13 @@ memory. A lower value can prevent THPs from being collapsed, resulting fewer pages being collapsed into THPs, and lower memory access performance. +``max_ptes_shared`` specifies how many pages can be shared across multiple +processes. Exceeding the number would block the collapse:: + + /sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_shared + +A higher value may increase memory footprint for some workloads. + Boot parameter ============== @@ -298,8 +310,7 @@ monitor how successfully the system is providing huge pages for use. thp_fault_alloc is incremented every time a huge page is successfully - allocated to handle a page fault. This applies to both the - first time a page is faulted and for COW faults. + allocated to handle a page fault. thp_collapse_alloc is incremented by khugepaged when it has found @@ -360,10 +371,9 @@ thp_split_pmd page table entry. thp_zero_page_alloc - is incremented every time a huge zero page is - successfully allocated. It includes allocations which where - dropped due race with other allocation. Note, it doesn't count - every map of the huge zero page, only its allocation. + is incremented every time a huge zero page used for thp is + successfully allocated. Note, it doesn't count every map of + the huge zero page, only its allocation. thp_zero_page_alloc_failed is incremented if kernel fails to allocate @@ -395,23 +405,8 @@ compact_fail is incremented if the system tries to compact memory but failed. -compact_pages_moved - is incremented each time a page is moved. If - this value is increasing rapidly, it implies that the system - is copying a lot of data to satisfy the huge page allocation. - It is possible that the cost of copying exceeds any savings - from reduced TLB misses. - -compact_pagemigrate_failed - is incremented when the underlying mechanism - for moving a page failed. - -compact_blocks_moved - is incremented each time memory compaction examines - a huge page aligned range of pages. - It is possible to establish how long the stalls were using the function -tracer to record how long was spent in __alloc_pages_nodemask and +tracer to record how long was spent in __alloc_pages() and using the mm_page_alloc tracepoint to identify which allocations were for huge pages. |