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Subject[PATCHv2, RFC 14/30] thp, mm: naive support of thp in generic read/write routines
Date
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

For now we still write/read at most PAGE_CACHE_SIZE bytes a time.

This implementation doesn't cover address spaces with backing store.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
mm/filemap.c | 35 ++++++++++++++++++++++++++++++-----
1 file changed, 30 insertions(+), 5 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index bdedb1b..79ba9cd 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1165,12 +1165,23 @@ find_page:
if (unlikely(page == NULL))
goto no_cached_page;
}
+ if (PageTransTail(page)) {
+ page_cache_release(page);
+ page = find_get_page(mapping,
+ index & ~HPAGE_CACHE_INDEX_MASK);
+ if (!PageTransHuge(page)) {
+ page_cache_release(page);
+ goto find_page;
+ }
+ }
if (PageReadahead(page)) {
+ BUG_ON(PageTransHuge(page));
page_cache_async_readahead(mapping,
ra, filp, page,
index, last_index - index);
}
if (!PageUptodate(page)) {
+ BUG_ON(PageTransHuge(page));
if (inode->i_blkbits == PAGE_CACHE_SHIFT ||
!mapping->a_ops->is_partially_uptodate)
goto page_not_up_to_date;
@@ -1212,18 +1223,25 @@ page_ok:
}
nr = nr - offset;

+ /* Recalculate offset in page if we've got a huge page */
+ if (PageTransHuge(page)) {
+ offset = (((loff_t)index << PAGE_CACHE_SHIFT) + offset);
+ offset &= ~HPAGE_PMD_MASK;
+ }
+
/* If users can be writing to this page using arbitrary
* virtual addresses, take care about potential aliasing
* before reading the page on the kernel side.
*/
if (mapping_writably_mapped(mapping))
- flush_dcache_page(page);
+ flush_dcache_page(page + (offset >> PAGE_CACHE_SHIFT));

/*
* When a sequential read accesses a page several times,
* only mark it as accessed the first time.
*/
- if (prev_index != index || offset != prev_offset)
+ if (prev_index != index ||
+ (offset & ~PAGE_CACHE_MASK) != prev_offset)
mark_page_accessed(page);
prev_index = index;

@@ -1238,8 +1256,9 @@ page_ok:
* "pos" here (the actor routine has to update the user buffer
* pointers and the remaining count).
*/
- ret = file_read_actor(desc, page, offset, nr);
- offset += ret;
+ ret = file_read_actor(desc, page + (offset >> PAGE_CACHE_SHIFT),
+ offset & ~PAGE_CACHE_MASK, nr);
+ offset = (offset & ~PAGE_CACHE_MASK) + ret;
index += offset >> PAGE_CACHE_SHIFT;
offset &= ~PAGE_CACHE_MASK;
prev_offset = offset;
@@ -2440,8 +2459,13 @@ again:
if (mapping_writably_mapped(mapping))
flush_dcache_page(page);

+ if (PageTransHuge(page))
+ offset = pos & ~HPAGE_PMD_MASK;
+
pagefault_disable();
- copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
+ copied = iov_iter_copy_from_user_atomic(
+ page + (offset >> PAGE_CACHE_SHIFT),
+ i, offset & ~PAGE_CACHE_MASK, bytes);
pagefault_enable();
flush_dcache_page(page);

@@ -2464,6 +2488,7 @@ again:
* because not all segments in the iov can be copied at
* once without a pagefault.
*/
+ offset = pos & ~PAGE_CACHE_MASK;
bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
iov_iter_single_seg_count(i));
goto again;
--
1.7.10.4


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