Re: [PATCHv6 08/37] filemap: handle huge pages in do_generic_file_read()
From: Matthew Wilcox <willy@infradead.org>
Date: 2017-02-09 21:55:05
Also in:
linux-ext4, linux-fsdevel, linux-mm, lkml
On Thu, Jan 26, 2017 at 02:57:50PM +0300, Kirill A. Shutemov wrote:
quoted hunk ↗ jump to hunk
+++ b/mm/filemap.c@@ -1886,6 +1886,7 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos, if (unlikely(page == NULL)) goto no_cached_page; } + page = compound_head(page);
We got this page from find_get_page(), which gets it from
pagecache_get_page(), which gets it from find_get_entry() ... which
(unless I'm lost in your patch series) returns the head page. So this
line is redundant, right?
But then down in filemap_fault, we have:
VM_BUG_ON_PAGE(page->index != offset, page);
... again, maybe I'm lost somewhere in your patch series, but I don't see
anywhere you remove that line (or modify it). So are you not testing
with VM debugging enabled, or are you not doing a test which includes
mapping a file with huge pages, reading from it (to get the page in cache),
then faulting on an address that is not in the first 4kB of that 2MB?