lkml.org 
[lkml]   [2019]   [Jul]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 1/3] mm/gup: introduce __put_user_pages()
Date
From: John Hubbard <jhubbard@nvidia.com>

Add a more capable variation of put_user_pages() to the
API set, and call it from the simple ones.

The new __put_user_pages() takes an enum that handles the various
combinations of needing to call set_page_dirty() or
set_page_dirty_lock(), before calling put_user_page().

Cc: Matthew Wilcox <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
include/linux/mm.h | 58 ++++++++++++++++++-
mm/gup.c | 137 ++++++++++++++++++++++-----------------------
2 files changed, 124 insertions(+), 71 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0334ca97c584..7218585681b2 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1057,8 +1057,62 @@ static inline void put_user_page(struct page *page)
put_page(page);
}

-void put_user_pages_dirty(struct page **pages, unsigned long npages);
-void put_user_pages_dirty_lock(struct page **pages, unsigned long npages);
+enum pup_flags_t {
+ PUP_FLAGS_CLEAN = 0,
+ PUP_FLAGS_DIRTY = 1,
+ PUP_FLAGS_LOCK = 2,
+ PUP_FLAGS_DIRTY_LOCK = 3,
+};
+
+void __put_user_pages(struct page **pages, unsigned long npages,
+ enum pup_flags_t flags);
+
+/**
+ * put_user_pages_dirty() - release and dirty an array of gup-pinned pages
+ * @pages: array of pages to be marked dirty and released.
+ * @npages: number of pages in the @pages array.
+ *
+ * "gup-pinned page" refers to a page that has had one of the get_user_pages()
+ * variants called on that page.
+ *
+ * For each page in the @pages array, make that page (or its head page, if a
+ * compound page) dirty, if it was previously listed as clean. Then, release
+ * the page using put_user_page().
+ *
+ * Please see the put_user_page() documentation for details.
+ *
+ * set_page_dirty(), which does not lock the page, is used here.
+ * Therefore, it is the caller's responsibility to ensure that this is
+ * safe. If not, then put_user_pages_dirty_lock() should be called instead.
+ *
+ */
+static inline void put_user_pages_dirty(struct page **pages,
+ unsigned long npages)
+{
+ __put_user_pages(pages, npages, PUP_FLAGS_DIRTY);
+}
+
+/**
+ * put_user_pages_dirty_lock() - release and dirty an array of gup-pinned pages
+ * @pages: array of pages to be marked dirty and released.
+ * @npages: number of pages in the @pages array.
+ *
+ * For each page in the @pages array, make that page (or its head page, if a
+ * compound page) dirty, if it was previously listed as clean. Then, release
+ * the page using put_user_page().
+ *
+ * Please see the put_user_page() documentation for details.
+ *
+ * This is just like put_user_pages_dirty(), except that it invokes
+ * set_page_dirty_lock(), instead of set_page_dirty().
+ *
+ */
+static inline void put_user_pages_dirty_lock(struct page **pages,
+ unsigned long npages)
+{
+ __put_user_pages(pages, npages, PUP_FLAGS_DIRTY_LOCK);
+}
+
void put_user_pages(struct page **pages, unsigned long npages);

#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
diff --git a/mm/gup.c b/mm/gup.c
index 98f13ab37bac..6831ef064d76 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -29,87 +29,86 @@ struct follow_page_context {
unsigned int page_mask;
};

-typedef int (*set_dirty_func_t)(struct page *page);
-
-static void __put_user_pages_dirty(struct page **pages,
- unsigned long npages,
- set_dirty_func_t sdf)
-{
- unsigned long index;
-
- for (index = 0; index < npages; index++) {
- struct page *page = compound_head(pages[index]);
-
- /*
- * Checking PageDirty at this point may race with
- * clear_page_dirty_for_io(), but that's OK. Two key cases:
- *
- * 1) This code sees the page as already dirty, so it skips
- * the call to sdf(). That could happen because
- * clear_page_dirty_for_io() called page_mkclean(),
- * followed by set_page_dirty(). However, now the page is
- * going to get written back, which meets the original
- * intention of setting it dirty, so all is well:
- * clear_page_dirty_for_io() goes on to call
- * TestClearPageDirty(), and write the page back.
- *
- * 2) This code sees the page as clean, so it calls sdf().
- * The page stays dirty, despite being written back, so it
- * gets written back again in the next writeback cycle.
- * This is harmless.
- */
- if (!PageDirty(page))
- sdf(page);
-
- put_user_page(page);
- }
-}
-
/**
- * put_user_pages_dirty() - release and dirty an array of gup-pinned pages
+ * __put_user_pages() - release an array of gup-pinned pages.
* @pages: array of pages to be marked dirty and released.
* @npages: number of pages in the @pages array.
+ * @flags: additional hints, to be applied to each page:
*
- * "gup-pinned page" refers to a page that has had one of the get_user_pages()
- * variants called on that page.
+ * PUP_FLAGS_CLEAN: no additional steps required. (Consider calling
+ * put_user_pages() directly, instead.)
*
- * For each page in the @pages array, make that page (or its head page, if a
- * compound page) dirty, if it was previously listed as clean. Then, release
- * the page using put_user_page().
+ * PUP_FLAGS_DIRTY: Call set_page_dirty() on the page (if not already
+ * dirty).
*
- * Please see the put_user_page() documentation for details.
+ * PUP_FLAGS_LOCK: meaningless by itself, but included in order to show
+ * the numeric relationship between the flags.
*
- * set_page_dirty(), which does not lock the page, is used here.
- * Therefore, it is the caller's responsibility to ensure that this is
- * safe. If not, then put_user_pages_dirty_lock() should be called instead.
+ * PUP_FLAGS_DIRTY_LOCK: Call set_page_dirty_lock() on the page (if not
+ * already dirty).
*
+ * For each page in the @pages array, release the page using put_user_page().
*/
-void put_user_pages_dirty(struct page **pages, unsigned long npages)
+void __put_user_pages(struct page **pages, unsigned long npages,
+ enum pup_flags_t flags)
{
- __put_user_pages_dirty(pages, npages, set_page_dirty);
-}
-EXPORT_SYMBOL(put_user_pages_dirty);
+ unsigned long index;

-/**
- * put_user_pages_dirty_lock() - release and dirty an array of gup-pinned pages
- * @pages: array of pages to be marked dirty and released.
- * @npages: number of pages in the @pages array.
- *
- * For each page in the @pages array, make that page (or its head page, if a
- * compound page) dirty, if it was previously listed as clean. Then, release
- * the page using put_user_page().
- *
- * Please see the put_user_page() documentation for details.
- *
- * This is just like put_user_pages_dirty(), except that it invokes
- * set_page_dirty_lock(), instead of set_page_dirty().
- *
- */
-void put_user_pages_dirty_lock(struct page **pages, unsigned long npages)
-{
- __put_user_pages_dirty(pages, npages, set_page_dirty_lock);
+ /*
+ * TODO: this can be optimized for huge pages: if a series of pages is
+ * physically contiguous and part of the same compound page, then a
+ * single operation to the head page should suffice.
+ */
+
+ for (index = 0; index < npages; index++) {
+ struct page *page = compound_head(pages[index]);
+
+ switch (flags) {
+ case PUP_FLAGS_CLEAN:
+ break;
+
+ case PUP_FLAGS_DIRTY:
+ /*
+ * Checking PageDirty at this point may race with
+ * clear_page_dirty_for_io(), but that's OK. Two key
+ * cases:
+ *
+ * 1) This code sees the page as already dirty, so it
+ * skips the call to set_page_dirty(). That could happen
+ * because clear_page_dirty_for_io() called
+ * page_mkclean(), followed by set_page_dirty().
+ * However, now the page is going to get written back,
+ * which meets the original intention of setting it
+ * dirty, so all is well: clear_page_dirty_for_io() goes
+ * on to call TestClearPageDirty(), and write the page
+ * back.
+ *
+ * 2) This code sees the page as clean, so it calls
+ * set_page_dirty(). The page stays dirty, despite being
+ * written back, so it gets written back again in the
+ * next writeback cycle. This is harmless.
+ */
+ if (!PageDirty(page))
+ set_page_dirty(page);
+ break;
+
+ case PUP_FLAGS_LOCK:
+ VM_WARN_ON_ONCE(flags == PUP_FLAGS_LOCK);
+ /*
+ * Shouldn't happen, but treat it as _DIRTY_LOCK if
+ * it does: fall through.
+ */
+
+ case PUP_FLAGS_DIRTY_LOCK:
+ /* Same comments as for PUP_FLAGS_DIRTY apply here. */
+ if (!PageDirty(page))
+ set_page_dirty_lock(page);
+ break;
+ };
+ put_user_page(page);
+ }
}
-EXPORT_SYMBOL(put_user_pages_dirty_lock);
+EXPORT_SYMBOL(__put_user_pages);

/**
* put_user_pages() - release an array of gup-pinned pages.
--
2.22.0
\
 
 \ /
  Last update: 2019-07-23 00:34    [W:0.135 / U:8.136 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site