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Subject[PATCHv6 14/22] thp, mm: allocate huge pages in grab_cache_page_write_begin()
Date
Try to allocate huge page if flags has AOP_FLAG_TRANSHUGE.

If, for some reason, it's not possible allocate a huge page at this
possition, it returns NULL. Caller should take care of fallback to
small pages.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
include/linux/fs.h | 1 +
mm/filemap.c | 23 +++++++++++++++++++++--
2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 26801f0bb1..42ccdeddd9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -282,6 +282,7 @@ enum positive_aop_returns {
#define AOP_FLAG_NOFS 0x0004 /* used by filesystem to direct
* helper code (eg buffer layer)
* to clear GFP_FS from alloc */
+#define AOP_FLAG_TRANSHUGE 0x0008 /* allocate transhuge page */

/*
* oh the beauties of C type declarations.
diff --git a/mm/filemap.c b/mm/filemap.c
index 3421bcaed4..410879a801 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2322,18 +2322,37 @@ struct page *grab_cache_page_write_begin(struct address_space *mapping,
gfp_t gfp_mask;
struct page *page;
gfp_t gfp_notmask = 0;
+ bool must_use_thp = (flags & AOP_FLAG_TRANSHUGE) &&
+ IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE);

gfp_mask = mapping_gfp_mask(mapping);
+ if (must_use_thp) {
+ BUG_ON(index & HPAGE_CACHE_INDEX_MASK);
+ BUG_ON(!(gfp_mask & __GFP_COMP));
+ }
if (mapping_cap_account_dirty(mapping))
gfp_mask |= __GFP_WRITE;
if (flags & AOP_FLAG_NOFS)
gfp_notmask = __GFP_FS;
repeat:
page = find_lock_page(mapping, index);
- if (page)
+ if (page) {
+ if (must_use_thp && !PageTransHuge(page)) {
+ unlock_page(page);
+ page_cache_release(page);
+ return NULL;
+ }
goto found;
+ }

- page = __page_cache_alloc(gfp_mask & ~gfp_notmask);
+ if (must_use_thp) {
+ page = alloc_pages(gfp_mask & ~gfp_notmask, HPAGE_PMD_ORDER);
+ if (page)
+ count_vm_event(THP_WRITE_ALLOC);
+ else
+ count_vm_event(THP_WRITE_ALLOC_FAILED);
+ } else
+ page = __page_cache_alloc(gfp_mask & ~gfp_notmask);
if (!page)
return NULL;
status = add_to_page_cache_lru(page, mapping, index,
--
1.8.4.rc3


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