The patch titled
Subject: mm/filemap: add mapping_seek_hole_data
has been added to the -mm tree. Its filename is
mm-filemap-add-mapping_seek_hole_data.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-filemap-add-mapping_seek_hole_data.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-filemap-add-mapping_seek_hole_data.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Subject: mm/filemap: add mapping_seek_hole_data
Rewrite shmem_seek_hole_data() and move it to filemap.c.
Link: https://lkml.kernel.org/r/20201112212641.27837-8-willy@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Dave Chinner <dchinner@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/pagemap.h | 2 +
mm/filemap.c | 75 ++++++++++++++++++++++++++++++++++++++
mm/shmem.c | 74 ++-----------------------------------
3 files changed, 81 insertions(+), 70 deletions(-)
--- a/include/linux/pagemap.h~mm-filemap-add-mapping_seek_hole_data
+++ a/include/linux/pagemap.h
@@ -761,6 +761,8 @@ extern void __delete_from_page_cache(str
int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask);
void delete_from_page_cache_batch(struct address_space *mapping,
struct pagevec *pvec);
+loff_t mapping_seek_hole_data(struct address_space *, loff_t start, loff_t end,
+ int whence);
/*
* Like add_to_page_cache_locked, but used to add newly allocated pages:
--- a/mm/filemap.c~mm-filemap-add-mapping_seek_hole_data
+++ a/mm/filemap.c
@@ -2586,6 +2586,81 @@ out:
}
EXPORT_SYMBOL(generic_file_read_iter);
+static inline bool page_seek_match(struct page *page, bool seek_data)
+{
+ if (xa_is_value(page) || PageUptodate(page))
+ return seek_data;
+ return !seek_data;
+}
+
+static inline
+unsigned int seek_page_size(struct xa_state *xas, struct page *page)
+{
+ if (xa_is_value(page))
+ return PAGE_SIZE << xa_get_order(xas->xa, xas->xa_index);
+ return thp_size(page);
+}
+
+/**
+ * mapping_seek_hole_data - Seek for SEEK_DATA / SEEK_HOLE in the page cache.
+ * @mapping: Address space to search.
+ * @start: First byte to consider.
+ * @end: Limit of search (exclusive).
+ * @whence: Either SEEK_HOLE or SEEK_DATA.
+ *
+ * If the page cache knows which blocks contain holes and which blocks
+ * contain data, your filesystem can use this function to implement
+ * SEEK_HOLE and SEEK_DATA. This is useful for filesystems which are
+ * entirely memory-based such as tmpfs, and filesystems which support
+ * unwritten extents.
+ *
+ * Return: The requested offset on successs, or -ENXIO if @whence specifies
+ * SEEK_DATA and there is no data after @start. There is an implicit hole
+ * after @end - 1, so SEEK_HOLE returns @end if all the bytes between @start
+ * and @end contain data.
+ */
+loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start,
+ loff_t end, int whence)
+{
+ XA_STATE(xas, &mapping->i_pages, start >> PAGE_SHIFT);
+ pgoff_t max = (end - 1) / PAGE_SIZE;
+ bool seek_data = (whence == SEEK_DATA);
+ struct page *page;
+
+ if (end <= start)
+ return -ENXIO;
+
+ rcu_read_lock();
+ while ((page = find_get_entry(&xas, max, XA_PRESENT))) {
+ loff_t pos = xas.xa_index * PAGE_SIZE;
+
+ if (start < pos) {
+ if (!seek_data)
+ goto unlock;
+ start = pos;
+ }
+
+ if (page_seek_match(page, seek_data))
+ goto unlock;
+ start = pos + seek_page_size(&xas, page);
+ put_page(page);
+ }
+ rcu_read_unlock();
+
+ if (seek_data)
+ return -ENXIO;
+ goto out;
+
+unlock:
+ rcu_read_unlock();
+ if (!xa_is_value(page))
+ put_page(page);
+out:
+ if (start > end)
+ return end;
+ return start;
+}
+
#ifdef CONFIG_MMU
#define MMAP_LOTSAMISS (100)
/*
--- a/mm/shmem.c~mm-filemap-add-mapping_seek_hole_data
+++ a/mm/shmem.c
@@ -2694,86 +2694,20 @@ static ssize_t shmem_file_read_iter(stru
return retval ? retval : error;
}
-/*
- * llseek SEEK_DATA or SEEK_HOLE through the page cache.
- */
-static pgoff_t shmem_seek_hole_data(struct address_space *mapping,
- pgoff_t index, pgoff_t end, int whence)
-{
- struct page *page;
- struct pagevec pvec;
- pgoff_t indices[PAGEVEC_SIZE];
- bool done = false;
- int i;
-
- pagevec_init(&pvec);
- pvec.nr = 1; /* start small: we may be there already */
- while (!done) {
- pvec.nr = find_get_entries(mapping, index,
- pvec.nr, pvec.pages, indices);
- if (!pvec.nr) {
- if (whence == SEEK_DATA)
- index = end;
- break;
- }
- for (i = 0; i < pvec.nr; i++, index++) {
- if (index < indices[i]) {
- if (whence == SEEK_HOLE) {
- done = true;
- break;
- }
- index = indices[i];
- }
- page = pvec.pages[i];
- if (page && !xa_is_value(page)) {
- if (!PageUptodate(page))
- page = NULL;
- }
- if (index >= end ||
- (page && whence == SEEK_DATA) ||
- (!page && whence == SEEK_HOLE)) {
- done = true;
- break;
- }
- }
- pagevec_remove_exceptionals(&pvec);
- pagevec_release(&pvec);
- pvec.nr = PAGEVEC_SIZE;
- cond_resched();
- }
- return index;
-}
-
static loff_t shmem_file_llseek(struct file *file, loff_t offset, int whence)
{
struct address_space *mapping = file->f_mapping;
struct inode *inode = mapping->host;
- pgoff_t start, end;
- loff_t new_offset;
if (whence != SEEK_DATA && whence != SEEK_HOLE)
return generic_file_llseek_size(file, offset, whence,
MAX_LFS_FILESIZE, i_size_read(inode));
+ if (offset < 0)
+ return -ENXIO;
+
inode_lock(inode);
/* We're holding i_mutex so we can access i_size directly */
-
- if (offset < 0 || offset >= inode->i_size)
- offset = -ENXIO;
- else {
- start = offset >> PAGE_SHIFT;
- end = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
- new_offset = shmem_seek_hole_data(mapping, start, end, whence);
- new_offset <<= PAGE_SHIFT;
- if (new_offset > offset) {
- if (new_offset < inode->i_size)
- offset = new_offset;
- else if (whence == SEEK_DATA)
- offset = -ENXIO;
- else
- offset = inode->i_size;
- }
- }
-
+ offset = mapping_seek_hole_data(mapping, offset, inode->i_size, whence);
if (offset >= 0)
offset = vfs_setpos(file, offset, MAX_LFS_FILESIZE);
inode_unlock(inode);
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are
mm-fix-readahead_page_batch-for-retry-entries.patch
mm-fix-madvise-willneed-performance-problem.patch
mm-page-flags-fix-comment.patch
mm-page_alloc-add-__free_pages-documentation.patch
mm-make-pagecache-tagged-lookups-return-only-head-pages.patch
mm-shmem-use-pagevec_lookup-in-shmem_unlock_mapping.patch
mm-swap-optimise-get_shadow_from_swap_cache.patch
mm-add-fgp_entry.patch
mm-filemap-rename-find_get_entry-to-mapping_get_entry.patch
mm-filemap-add-helper-for-finding-pages.patch
mm-filemap-add-mapping_seek_hole_data.patch
iomap-use-mapping_seek_hole_data.patch
mm-add-and-use-find_lock_entries.patch
mm-add-an-end-parameter-to-find_get_entries.patch
mm-add-an-end-parameter-to-pagevec_lookup_entries.patch
mm-remove-nr_entries-parameter-from-pagevec_lookup_entries.patch
mm-pass-pvec-directly-to-find_get_entries.patch
mm-remove-pagevec_lookup_entries.patch
mm-truncateshmem-handle-truncates-that-split-thps.patch
mm-filemap-return-only-head-pages-from-find_get_entries.patch
mm-introduce-memfd_secret-system-call-to-create-secret-memory-areas-fix.patch
