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Diffstat (limited to 'Documentation/vm/transhuge.txt')
| -rw-r--r-- | Documentation/vm/transhuge.txt | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt index 21cf34f3ddb2..d9cb65cf5cfd 100644 --- a/Documentation/vm/transhuge.txt +++ b/Documentation/vm/transhuge.txt @@ -113,9 +113,26 @@ guaranteed, but it may be more likely in case the allocation is for a MADV_HUGEPAGE region. echo always >/sys/kernel/mm/transparent_hugepage/defrag +echo defer >/sys/kernel/mm/transparent_hugepage/defrag echo madvise >/sys/kernel/mm/transparent_hugepage/defrag echo never >/sys/kernel/mm/transparent_hugepage/defrag +"always" means that an application requesting THP will stall on allocation +failure and directly reclaim pages and compact memory in an effort to +allocate a THP immediately. This may be desirable for virtual machines +that benefit heavily from THP use and are willing to delay the VM start +to utilise them. + +"defer" means that an application will wake kswapd in the background +to reclaim pages and wake kcompact to compact memory so that THP is +available in the near future. It's the responsibility of khugepaged +to then install the THP pages later. + +"madvise" will enter direct reclaim like "always" but only for regions +that are have used madvise(MADV_HUGEPAGE). This is the default behaviour. + +"never" should be self-explanatory. + By default kernel tries to use huge zero page on read page fault. It's possible to disable huge zero page by writing 0 or enable it back by writing 1: @@ -229,6 +246,11 @@ thp_split_page is incremented every time a huge page is split into base thp_split_page_failed is is incremented if kernel fails to split huge page. This can happen if the page was pinned by somebody. +thp_deferred_split_page is incremented when a huge page is put onto split + queue. This happens when a huge page is partially unmapped and + splitting it would free up some memory. Pages on split queue are + going to be split under memory pressure. + thp_split_pmd is incremented every time a PMD split into table of PTEs. This can happen, for instance, when application calls mprotect() or munmap() on part of huge page. It doesn't split huge page, only |