From: Matthew Wilcox <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
William Kucharski <william.kucharski@oracle.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Yang Shi <yang.shi@linux.alibaba.com>,
Dave Chinner <dchinner@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 04/12] mm/filemap: Add mapping_seek_hole_data
Date: Tue, 29 Sep 2020 13:42:51 +0100 [thread overview]
Message-ID: <20200929124251.GB20115@casper.infradead.org> (raw)
In-Reply-To: <20200929084653.GC10896@quack2.suse.cz>
On Tue, Sep 29, 2020 at 10:46:53AM +0200, Jan Kara wrote:
> On Mon 14-09-20 14:00:34, Matthew Wilcox (Oracle) wrote:
> > Rewrite shmem_seek_hole_data() and move it to filemap.c.
> >
> > + rcu_read_lock();
> > + while ((page = xas_find_get_entry(&xas, max, XA_PRESENT))) {
> > + loff_t pos = xas.xa_index * PAGE_SIZE;
>
> OK, but for ordinary filesystems this could be problematic because of
> exceptional entries?
For ordinary filesystems, I have this queued up on top:
http://git.infradead.org/users/willy/pagecache.git/commitdiff/02c740b215bab901f95a560759b3bd906648da08
which handles exceptional entries. It treats shadow/swap/DAX entries
the same -- there's definitely data there, it's just not in a struct
page right now.
> Also for shmem you've dropped the PageUptodate check which I'm not sure is
> safe?
That was unintentional. I did run xfstests against this patch (just did
it again ... it passes), so I suspect it doesn't create a !Uptodate page.
I'll see if I can enhance the existing xfstests to catch this case.
The patch I link to above also doesn't handle !Uptodate pages on shmem
filesystems the same way that the current code does. So ... on top of
this patch, I propose doing this:
@@ -2416,6 +2416,14 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_ite
r *iter)
}
EXPORT_SYMBOL(generic_file_read_iter);
+static inline loff_t page_seek_hole_data(struct page *page,
+ loff_t start, loff_t end, bool seek_data)
+{
+ if (xa_is_value(page) || PageUptodate(page))
+ return seek_data ? start : end;
+ return seek_data ? end : start;
+}
+
static inline
unsigned int seek_page_size(struct xa_state *xas, struct page *page)
{
@@ -2463,10 +2471,10 @@ loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start,
start = pos;
}
- if (seek_data)
+ pos += seek_page_size(&xas, page);
+ start = page_seek_hole_data(page, start, pos, seek_data);
+ if (start < pos)
goto unlock;
-
- start = pos + seek_page_size(&xas, page);
}
rcu_read_unlock();
... and then rebasing the other patch on top of this works out nicely.
Here's the result:
http://git.infradead.org/users/willy/pagecache.git/commitdiff/9eb3f496b7cdcdcae83026e861e148f46921c367
http://git.infradead.org/users/willy/pagecache.git/commitdiff/7d93274088f0872d849a906d783dc260bee106b9
next prev parent reply other threads:[~2020-09-29 12:43 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-14 13:00 [PATCH v2 00/12] Overhaul multi-page lookups for THP Matthew Wilcox (Oracle)
2020-09-14 13:00 ` [PATCH v2 01/12] mm: Make pagecache tagged lookups return only head pages Matthew Wilcox (Oracle)
2020-09-29 9:13 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 02/12] mm/shmem: Use pagevec_lookup in shmem_unlock_mapping Matthew Wilcox (Oracle)
2020-09-29 8:28 ` Jan Kara
2020-09-29 18:36 ` Matthew Wilcox
2020-09-14 13:00 ` [PATCH v2 03/12] mm/filemap: Add helper for finding pages Matthew Wilcox (Oracle)
2020-09-29 8:27 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 04/12] mm/filemap: Add mapping_seek_hole_data Matthew Wilcox (Oracle)
2020-09-29 8:46 ` Jan Kara
2020-09-29 12:42 ` Matthew Wilcox [this message]
2020-09-29 13:39 ` Matthew Wilcox
2020-09-14 13:00 ` [PATCH v2 05/12] mm: Add and use find_lock_entries Matthew Wilcox (Oracle)
2020-09-29 8:58 ` Jan Kara
2020-09-29 12:48 ` Matthew Wilcox
2020-09-30 10:40 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 06/12] mm: Add an 'end' parameter to find_get_entries Matthew Wilcox (Oracle)
2020-09-14 13:00 ` [PATCH v2 07/12] mm: Add an 'end' parameter to pagevec_lookup_entries Matthew Wilcox (Oracle)
2020-09-29 9:02 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 08/12] mm: Remove nr_entries parameter from pagevec_lookup_entries Matthew Wilcox (Oracle)
2020-09-29 9:03 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 09/12] mm: Pass pvec directly to find_get_entries Matthew Wilcox (Oracle)
2020-09-29 9:07 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 10/12] mm: Remove pagevec_lookup_entries Matthew Wilcox (Oracle)
2020-09-29 9:08 ` Jan Kara
2020-09-14 13:00 ` [PATCH v2 11/12] mm/truncate,shmem: Handle truncates that split THPs Matthew Wilcox (Oracle)
2020-09-30 11:59 ` Jan Kara
2020-09-30 14:51 ` Matthew Wilcox
2020-09-14 13:00 ` [PATCH v2 12/12] mm/filemap: Return only head pages from find_get_entries Matthew Wilcox (Oracle)
2020-09-30 12:15 ` Jan Kara
2020-09-30 12:36 ` Matthew Wilcox
2020-09-30 17:08 ` Jan Kara
2020-09-30 17:23 ` Matthew Wilcox
2020-10-01 7:17 ` Jan Kara
2020-10-25 23:19 ` Matthew Wilcox
2020-10-26 9:11 ` Jan Kara
2020-09-28 20:13 ` [PATCH v2 00/12] Overhaul multi-page lookups for THP Matthew Wilcox
2020-09-29 8:50 ` William Kucharski
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