admin-guide/mm/transhuge.rst

11 using huge pages for the backing of virtual memory with huge pages
51 increments of a power-of-2 number of pages. mTHP can back anonymous
66 collapses sequences of basic pages into PMD-sized huge pages.
150 pages unless hugepages are immediately available. Clearly if we spend CPU
152 use hugepages later instead of regular pages. This isn't always
166 	allocation failure and directly reclaim pages and compact
173 	to reclaim pages and wake kcompactd to compact memory so that
175 	of khugepaged to then install the THP pages later.
181 	pages and wake kcompactd to compact memory so that THP is
207 "underused". A THP is underused if the number of zero-filled pages in
238 You can also control how many pages khugepaged should scan at each
253 The khugepaged progress can be seen in the number of pages collapsed (note
254 that this counter may not be an exact count of the number of pages
256 being replaced by a PMD mapping, or (2) All 4K physical pages replaced by
268 ``max_ptes_none`` specifies how many extra small pages (that are
270 of small pages into one large page::
279 ``max_ptes_swap`` specifies how many pages can be brought in from
280 swap when collapsing a group of pages into a transparent huge page::
286 collapsed, resulting fewer pages being collapsed into
289 ``max_ptes_shared`` specifies how many pages can be shared across multiple
290 processes. khugepaged might treat pages of THPs as shared if any page of
336     Attempt to allocate huge pages every time we need a new page;
339     Do not allocate huge pages;
346     Only allocate huge pages if requested with fadvise()/madvise();
351 ``huge=never`` will not attempt to break up huge pages at all, just stop more
377     Attempt to allocate <size> huge pages every time we need a new page;
384     Do not allocate <size> huge pages;
391     Only allocate <size> huge pages if requested with fadvise()/madvise();
405 The number of PMD-sized anonymous transparent huge pages currently used by the
408 pages, it is necessary to read ``/proc/PID/smaps`` and count the AnonHugePages
413 The number of file transparent huge pages mapped to userspace is available
415 To identify what applications are mapping file transparent huge pages, it
423 monitor how successfully the system is providing huge pages for use.
431 	a range of pages to collapse into one huge page and has
436 	a huge page and instead falls back to using small pages.
440 	instead falls back to using small pages even though the
445 	of pages that should be collapsed into one huge page but failed
455 	but fails and instead falls back to using small pages. (Note that
460 	falls back to using small pages even though the allocation was
470 	pages. This can happen for a variety of reasons but a common
481 	splitting it would free up some memory. Pages on split queue are
487 	zero pages in the THP is above a certain threshold
503 	huge zero page and falls back to using small pages.
516 monitor the system's effectiveness in providing huge pages for usage. Each
525 	a huge page and instead falls back to using huge pages with
526 	lower orders or small pages.
530 	instead falls back to using huge pages with lower orders or
531 	small pages even though the allocation was successful.
548 	but fails and instead falls back to using small pages.
552 	falls back to using small pages even though the allocation was
567         it would free up some memory. Pages on split queue are going to
582 As the system ages, allocating huge pages may be expensive as the
602 for huge pages.