Now that pages are "DMA-pinned" via pin_user_page*(), and unpinned via unpin_user_pages*(), we need some visibility into whether all of this is working correctly. Add two new fields to /proc/vmstat: nr_foll_pin_acquired nr_foll_pin_released These are documented in Documentation/core-api/pin_user_pages.rst. They represent the number of pages (since boot time) that have been pinned ("nr_foll_pin_acquired") and unpinned ("nr_foll_pin_released"), via pin_user_pages*() and unpin_user_pages*(). In the absence of long-running DMA or RDMA operations that hold pages pinned, the above two fields will normally be equal to each other. Also: update Documentation/core-api/pin_user_pages.rst, to remove an earlier (now confirmed untrue) claim about a performance problem with /proc/vmstat. Also: updated Documentation/core-api/pin_user_pages.rst to rename the new /proc/vmstat entries, to the names listed here. Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx> --- Documentation/core-api/pin_user_pages.rst | 8 ++------ include/linux/mmzone.h | 2 ++ mm/gup.c | 10 ++++++++++ mm/vmstat.c | 2 ++ 4 files changed, 16 insertions(+), 6 deletions(-) diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst index dd21ea140ef4..194204d74a50 100644 --- a/Documentation/core-api/pin_user_pages.rst +++ b/Documentation/core-api/pin_user_pages.rst @@ -208,12 +208,8 @@ has the following new calls to exercise the new pin*() wrapper functions: You can monitor how many total dma-pinned pages have been acquired and released since the system was booted, via two new /proc/vmstat entries: :: - /proc/vmstat/nr_foll_pin_requested - /proc/vmstat/nr_foll_pin_requested - -Those are both going to show zero, unless CONFIG_DEBUG_VM is set. This is -because there is a noticeable performance drop in unpin_user_page(), when they -are activated. + /proc/vmstat/nr_foll_pin_acquired + /proc/vmstat/nr_foll_pin_released Other diagnostics ================= diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 462f6873905a..4bca42eeb439 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -243,6 +243,8 @@ enum node_stat_item { NR_DIRTIED, /* page dirtyings since bootup */ NR_WRITTEN, /* page writings since bootup */ NR_KERNEL_MISC_RECLAIMABLE, /* reclaimable non-slab kernel pages */ + NR_FOLL_PIN_ACQUIRED, /* via: pin_user_page(), gup flag: FOLL_PIN */ + NR_FOLL_PIN_RELEASED, /* pages returned via unpin_user_page() */ NR_VM_NODE_STAT_ITEMS }; diff --git a/mm/gup.c b/mm/gup.c index 4d0d94405639..7c543849181b 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -86,6 +86,8 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page, if (flags & FOLL_GET) return try_get_compound_head(page, refs); else if (flags & FOLL_PIN) { + int orig_refs = refs; + /* * When pinning a compound page of order > 1 (which is what * hpage_pincount_available() checks for), use an exact count to @@ -104,6 +106,9 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page, if (hpage_pincount_available(page)) hpage_pincount_add(page, refs); + mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, + orig_refs); + return page; } @@ -158,6 +163,8 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags) * once, so that the page really is pinned. */ page_ref_add(page, refs); + + mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1); } return true; @@ -178,6 +185,7 @@ static bool __unpin_devmap_managed_user_page(struct page *page) count = page_ref_sub_return(page, refs); + mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1); /* * devmap page refcounts are 1-based, rather than 0-based: if * refcount is 1, then the page is free and the refcount is @@ -228,6 +236,8 @@ void unpin_user_page(struct page *page) if (page_ref_sub_and_test(page, refs)) __put_page(page); + + mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1); } EXPORT_SYMBOL(unpin_user_page); diff --git a/mm/vmstat.c b/mm/vmstat.c index 78d53378db99..c9c0d71f917f 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1168,6 +1168,8 @@ const char * const vmstat_text[] = { "nr_dirtied", "nr_written", "nr_kernel_misc_reclaimable", + "nr_foll_pin_acquired", + "nr_foll_pin_released", /* enum writeback_stat_item counters */ "nr_dirty_threshold", -- 2.25.0