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Diffstat (limited to 'Documentation/admin-guide/mm/transhuge.rst')
| -rw-r--r-- | Documentation/admin-guide/mm/transhuge.rst | 85 |
1 files changed, 68 insertions, 17 deletions
diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index d414d3f5592a..058485daf186 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -202,12 +202,11 @@ PMD-mappable transparent hugepage:: cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size -khugepaged will be automatically started when one or more hugepage -sizes are enabled (either by directly setting "always" or "madvise", -or by setting "inherit" while the top-level enabled is set to "always" -or "madvise"), and it'll be automatically shutdown when the last -hugepage size is disabled (either by directly setting "never", or by -setting "inherit" while the top-level enabled is set to "never"). +khugepaged will be automatically started when PMD-sized THP is enabled +(either of the per-size anon control or the top-level control are set +to "always" or "madvise"), and it'll be automatically shutdown when +PMD-sized THP is disabled (when both the per-size anon control and the +top-level control are "never") Khugepaged controls ------------------- @@ -332,6 +331,31 @@ deny force Force the huge option on for all - very useful for testing; +Shmem can also use "multi-size THP" (mTHP) by adding a new sysfs knob to +control mTHP allocation: +'/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/shmem_enabled', +and its value for each mTHP is essentially consistent with the global +setting. An 'inherit' option is added to ensure compatibility with these +global settings. Conversely, the options 'force' and 'deny' are dropped, +which are rather testing artifacts from the old ages. + +always + Attempt to allocate <size> huge pages every time we need a new page; + +inherit + Inherit the top-level "shmem_enabled" value. By default, PMD-sized hugepages + have enabled="inherit" and all other hugepage sizes have enabled="never"; + +never + Do not allocate <size> huge pages; + +within_size + Only allocate <size> huge page if it will be fully within i_size. + Also respect fadvise()/madvise() hints; + +advise + Only allocate <size> huge pages if requested with fadvise()/madvise(); + Need of application restart =========================== @@ -344,10 +368,6 @@ also applies to the regions registered in khugepaged. Monitoring usage ================ -.. note:: - Currently the below counters only record events relating to - PMD-sized THP. Events relating to other THP sizes are not included. - The number of PMD-sized anonymous transparent huge pages currently used by the system is available by reading the AnonHugePages field in ``/proc/meminfo``. To identify what applications are using PMD-sized anonymous transparent huge @@ -392,20 +412,23 @@ thp_collapse_alloc_failed the allocation. thp_file_alloc - is incremented every time a file huge page is successfully - allocated. + is incremented every time a shmem huge page is successfully + allocated (Note that despite being named after "file", the counter + measures only shmem). 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. + is incremented if a shmem huge page is attempted to be allocated + but fails and instead falls back to using small pages. (Note that + despite being named after "file", the counter measures only shmem). thp_file_fallback_charge - is incremented if a file huge page cannot be charged and instead + is incremented if a shmem huge page cannot be charged and instead falls back to using small pages even though the allocation was - successful. + successful. (Note that despite being named after "file", the + counter measures only shmem). thp_file_mapped - is incremented every time a file huge page is mapped into + is incremented every time a file or shmem huge page is mapped into user address space. thp_split_page @@ -476,6 +499,34 @@ swpout_fallback Usually because failed to allocate some continuous swap space for the huge page. +shmem_alloc + is incremented every time a shmem huge page is successfully + allocated. + +shmem_fallback + is incremented if a shmem huge page is attempted to be allocated + but fails and instead falls back to using small pages. + +shmem_fallback_charge + is incremented if a shmem huge page cannot be charged and instead + falls back to using small pages even though the allocation was + successful. + +split + is incremented every time a huge page is successfully split into + smaller orders. This can happen for a variety of reasons but a + common reason is that a huge page is old and is being reclaimed. + +split_failed + is incremented if kernel fails to split huge + page. This can happen if the page was pinned by somebody. + +split_deferred + 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, if splitting is possible. + As the system ages, allocating huge pages may be expensive as the system uses memory compaction to copy data around memory to free a huge page for use. There are some counters in ``/proc/vmstat`` to help |