Most page cache allocation happens via readahead (sync or async), so if
we want to have significant number of huge pages in page cache we need
to find a ways to allocate them from readahead.
Unfortunately, huge pages doesn't fit into current readahead design:
128 max readahead window, assumption on page size, PageReadahead() to
track hit/miss.
I haven't found a ways to get it right yet.
This patch just allocates huge page if allowed, but doesn't really
provide any readahead if huge page is allocated. We read out 2M a time
and I would expect spikes in latancy without readahead.
Therefore HACK.
Any suggestions are welcome.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
mm/readahead.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/mm/readahead.c b/mm/readahead.c
index 65ec288dc057..3d7742a687f2 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -173,6 +173,20 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
if (page_offset > end_index)
break;
+ if ((!page_idx || page_offset % HPAGE_PMD_NR == 0) &&
+ page_cache_allow_huge(mapping, page_offset)) {
+ page = __page_cache_alloc_order(gfp_mask | __GFP_COMP,
+ HPAGE_PMD_ORDER);
+ if (page) {
+ prep_transhuge_page(page);
+ page->index = round_down(page_offset,
+ HPAGE_PMD_NR);
+ list_add(&page->lru, &page_pool);
+ ret++;
+ goto start_io;
+ }
+ }
+
rcu_read_lock();
page = radix_tree_lookup(&mapping->page_tree, page_offset);
rcu_read_unlock();
@@ -188,7 +202,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
SetPageReadahead(page);
ret++;
}
-
+start_io:
/*
* Now start the IO. We ignore I/O errors - if the page is not
* uptodate then the caller will launch readpage again, and
--
2.8.1
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