| Message ID | 20200211001536.1027652-9-jhubbard@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/gup: track FOLL_PIN pages | expand |
On Mon 10-02-20 16:15:32, John Hubbard wrote: > 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. > > Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Signed-off-by: John Hubbard <jhubbard@nvidia.com> The patch looks good to me now. You can add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > Documentation/core-api/pin_user_pages.rst | 33 +++++++++++++++++++---- > include/linux/mmzone.h | 2 ++ > mm/gup.c | 13 +++++++++ > mm/vmstat.c | 2 ++ > 4 files changed, 45 insertions(+), 5 deletions(-) > > diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst > index 7e5dd8b1b3f2..5c8a5f89756b 100644 > --- a/Documentation/core-api/pin_user_pages.rst > +++ b/Documentation/core-api/pin_user_pages.rst > @@ -208,12 +208,35 @@ 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 > + /proc/vmstat/nr_foll_pin_acquired > + /proc/vmstat/nr_foll_pin_released > > -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. > +Under normal conditions, these two values will be equal unless there are any > +long-term [R]DMA pins in place, or during pin/unpin transitions. > + > +* nr_foll_pin_acquired: This is the number of logical pins that have been > + acquired since the system was powered on. For huge pages, the head page is > + pinned once for each page (head page and each tail page) within the huge page. > + This follows the same sort of behavior that get_user_pages() uses for huge > + pages: the head page is refcounted once for each tail or head page in the huge > + page, when get_user_pages() is applied to a huge page. > + > +* nr_foll_pin_released: The number of logical pins that have been released since > + the system was powered on. Note that pages are released (unpinned) on a > + PAGE_SIZE granularity, even if the original pin was applied to a huge page. > + Becaused of the pin count behavior described above in "nr_foll_pin_acquired", > + the accounting balances out, so that after doing this:: > + > + pin_user_pages(huge_page); > + for (each page in huge_page) > + unpin_user_page(page); > + > +...the following is expected:: > + > + nr_foll_pin_released == nr_foll_pin_acquired > + > +(...unless it was already out of balance due to a long-term RDMA pin being in > +place.) > > References > ========== > 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..441f7a48f370 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); > > @@ -2259,6 +2269,9 @@ static int record_subpages(struct page *page, unsigned long addr, > static void put_compound_head(struct page *page, int refs, unsigned int flags) > { > if (flags & FOLL_PIN) { > + mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, > + refs); > + > if (hpage_pincount_available(page)) > hpage_pincount_sub(page, refs); > else > 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 >
diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst index 7e5dd8b1b3f2..5c8a5f89756b 100644 --- a/Documentation/core-api/pin_user_pages.rst +++ b/Documentation/core-api/pin_user_pages.rst @@ -208,12 +208,35 @@ 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 + /proc/vmstat/nr_foll_pin_acquired + /proc/vmstat/nr_foll_pin_released -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. +Under normal conditions, these two values will be equal unless there are any +long-term [R]DMA pins in place, or during pin/unpin transitions. + +* nr_foll_pin_acquired: This is the number of logical pins that have been + acquired since the system was powered on. For huge pages, the head page is + pinned once for each page (head page and each tail page) within the huge page. + This follows the same sort of behavior that get_user_pages() uses for huge + pages: the head page is refcounted once for each tail or head page in the huge + page, when get_user_pages() is applied to a huge page. + +* nr_foll_pin_released: The number of logical pins that have been released since + the system was powered on. Note that pages are released (unpinned) on a + PAGE_SIZE granularity, even if the original pin was applied to a huge page. + Becaused of the pin count behavior described above in "nr_foll_pin_acquired", + the accounting balances out, so that after doing this:: + + pin_user_pages(huge_page); + for (each page in huge_page) + unpin_user_page(page); + +...the following is expected:: + + nr_foll_pin_released == nr_foll_pin_acquired + +(...unless it was already out of balance due to a long-term RDMA pin being in +place.) References ========== 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..441f7a48f370 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); @@ -2259,6 +2269,9 @@ static int record_subpages(struct page *page, unsigned long addr, static void put_compound_head(struct page *page, int refs, unsigned int flags) { if (flags & FOLL_PIN) { + mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, + refs); + if (hpage_pincount_available(page)) hpage_pincount_sub(page, refs); else 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",
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. Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> --- Documentation/core-api/pin_user_pages.rst | 33 +++++++++++++++++++---- include/linux/mmzone.h | 2 ++ mm/gup.c | 13 +++++++++ mm/vmstat.c | 2 ++ 4 files changed, 45 insertions(+), 5 deletions(-)