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Message-ID: <20200912032042.GA6583@casper.infradead.org>
Date: Sat, 12 Sep 2020 04:20:42 +0100
From: Matthew Wilcox <willy@...radead.org>
To: linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>,
William Kucharski <william.kucharski@...cle.com>,
Jani Nikula <jani.nikula@...ux.intel.com>,
Alexey Dobriyan <adobriyan@...il.com>,
Johannes Weiner <hannes@...xchg.org>,
Chris Wilson <chris@...is-wilson.co.uk>,
Matthew Auld <matthew.auld@...el.com>,
Huang Ying <ying.huang@...el.com>,
intel-gfx@...ts.freedesktop.org, cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 7/8] mm/shmem: Return head page from find_lock_entry
On Thu, Sep 10, 2020 at 07:33:17PM +0100, Matthew Wilcox (Oracle) wrote:
> Convert shmem_getpage_gfp() (the only remaining caller of
> find_lock_entry()) to cope with a head page being returned instead of
> the subpage for the index.
This version was buggy. Apparently I was too focused on running the test suite against XFS and neglected to run it against tmpfs, which crashed instantly.
Here's the patch I should have sent.
commit 7bfa655881da76f3386e6d4c07e38a165b4a6ca8
Author: Matthew Wilcox (Oracle) <willy@...radead.org>
Date: Sun Aug 2 07:22:34 2020 -0400
mm/shmem: Return head page from find_lock_entry
Convert shmem_getpage_gfp() (the only remaining caller of
find_lock_entry()) to cope with a head page being returned instead of
the subpage for the index.
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 905a64030647..f374618b2c93 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -371,6 +371,15 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
mapping_gfp_mask(mapping));
}
+/* Does this page contain this index? */
+static inline bool thp_contains(struct page *head, pgoff_t index)
+{
+ /* HugeTLBfs indexes the page cache in units of hpage_size */
+ if (PageHuge(head))
+ return head->index == index;
+ return page_index(head) == (index & ~(thp_nr_pages(head) - 1UL));
+}
+
/*
* Given the page we found in the page cache, return the page corresponding
* to this index in the file
diff --git a/mm/filemap.c b/mm/filemap.c
index 2f134383b0ae..453535170b8d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1614,37 +1614,34 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t index)
}
/**
- * find_lock_entry - locate, pin and lock a page cache entry
- * @mapping: the address_space to search
- * @offset: the page cache index
+ * find_lock_entry - Locate and lock a page cache entry.
+ * @mapping: The address_space to search.
+ * @index: The page cache index.
*
- * Looks up the page cache slot at @mapping & @offset. If there is a
- * page cache page, it is returned locked and with an increased
- * refcount.
+ * Looks up the page at @mapping & @index. If there is a page in the
+ * cache, the head page is returned locked and with an increased refcount.
*
* If the slot holds a shadow entry of a previously evicted page, or a
* swap entry from shmem/tmpfs, it is returned.
*
- * find_lock_entry() may sleep.
- *
- * Return: the found page or shadow entry, %NULL if nothing is found.
+ * Context: May sleep.
+ * Return: The head page or shadow entry, %NULL if nothing is found.
*/
-struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset)
+struct page *find_lock_entry(struct address_space *mapping, pgoff_t index)
{
struct page *page;
repeat:
- page = find_get_entry(mapping, offset);
+ page = find_get_entry(mapping, index);
if (page && !xa_is_value(page)) {
lock_page(page);
/* Has the page been truncated? */
- if (unlikely(page_mapping(page) != mapping)) {
+ if (unlikely(page->mapping != mapping)) {
unlock_page(page);
put_page(page);
goto repeat;
}
- page = find_subpage(page, offset);
- VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
+ VM_BUG_ON_PAGE(!thp_contains(page, index), page);
}
return page;
}
diff --git a/mm/shmem.c b/mm/shmem.c
index 271548ca20f3..58bc9e326d0d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1822,6 +1822,8 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
return error;
}
+ if (page)
+ hindex = page->index;
if (page && sgp == SGP_WRITE)
mark_page_accessed(page);
@@ -1832,11 +1834,10 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
unlock_page(page);
put_page(page);
page = NULL;
+ hindex = index;
}
- if (page || sgp == SGP_READ) {
- *pagep = page;
- return 0;
- }
+ if (page || sgp == SGP_READ)
+ goto out;
/*
* Fast cache lookup did not find it:
@@ -1961,14 +1962,13 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
* it now, lest undo on failure cancel our earlier guarantee.
*/
if (sgp != SGP_WRITE && !PageUptodate(page)) {
- struct page *head = compound_head(page);
int i;
- for (i = 0; i < compound_nr(head); i++) {
- clear_highpage(head + i);
- flush_dcache_page(head + i);
+ for (i = 0; i < compound_nr(page); i++) {
+ clear_highpage(page + i);
+ flush_dcache_page(page + i);
}
- SetPageUptodate(head);
+ SetPageUptodate(page);
}
/* Perhaps the file has been truncated since we checked */
@@ -1984,6 +1984,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
error = -EINVAL;
goto unlock;
}
+out:
*pagep = page + index - hindex;
return 0;
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