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Diffstat (limited to '')
| -rw-r--r-- | Documentation/admin-guide/mm/transhuge.rst | 57 |
1 files changed, 34 insertions, 23 deletions
diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index bd5714547cee..8ee78ec232eb 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -191,7 +191,14 @@ 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 +227,13 @@ 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 +312,7 @@ 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 @@ -310,6 +323,11 @@ thp_fault_fallback is incremented if a page fault fails to allocate a huge page and instead falls back to using small pages. +thp_fault_fallback_charge + is incremented if a page fault fails to charge a huge page and + instead falls back to using small pages even though the + allocation was successful. + thp_collapse_alloc_failed is incremented if khugepaged found a range of pages that should be collapsed into one huge page but failed @@ -319,6 +337,15 @@ thp_file_alloc is incremented every time a file huge page is successfully allocated. +thp_file_fallback + is incremented if a file huge page is attempted to be allocated + but fails and instead falls back to using small pages. + +thp_file_fallback_charge + is incremented if a file huge page cannot be charged and instead + falls back to using small pages even though the allocation was + successful. + thp_file_mapped is incremented every time a file huge page is mapped into user address space. @@ -346,10 +373,9 @@ 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 @@ -381,23 +407,8 @@ 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. |