From: Matthew Wilcox <willy@infradead.org>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
William Kucharski <william.kucharski@oracle.com>,
Christoph Hellwig <hch@lst.de>, Jan Kara <jack@suse.cz>,
Dave Chinner <dchinner@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Yang Shi <yang.shi@linux.alibaba.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH 2/2] mm/filemap: fix mapping_seek_hole_data on THP & 32-bit
Date: Thu, 22 Apr 2021 02:16:31 +0100 [thread overview]
Message-ID: <20210422011631.GL3596236@casper.infradead.org> (raw)
In-Reply-To: <alpine.LSU.2.11.2104211737410.3299@eggly.anvils>
On Wed, Apr 21, 2021 at 05:39:14PM -0700, Hugh Dickins wrote:
> No problem on 64-bit without huge pages, but xfstests generic/285
> and other SEEK_HOLE/SEEK_DATA tests have regressed on huge tmpfs,
> and on 32-bit architectures, with the new mapping_seek_hole_data().
> Several different bugs turned out to need fixing.
>
> u64 casts added to stop unfortunate sign-extension when shifting
> (and let's use shifts throughout, rather than mixed with * and /).
That confuses me. loff_t is a signed long long, but it can't be negative
(... right?) So how does casting it to an u64 before dividing by
PAGE_SIZE help?
> Use round_up() when advancing pos, to stop assuming that pos was
> already THP-aligned when advancing it by THP-size. (But I believe
> this use of round_up() assumes that any THP must be THP-aligned:
> true while tmpfs enforces that alignment, and is the only fs with
> FS_THP_SUPPORT; but might need to be generalized in the future?
> If I try to generalize it right now, I'm sure to get it wrong!)
No generalisation needed in future. Folios must be naturally aligned
within a file.
> @@ -2681,7 +2681,8 @@ loff_t mapping_seek_hole_data(struct add
>
> rcu_read_lock();
> while ((page = find_get_entry(&xas, max, XA_PRESENT))) {
> - loff_t pos = xas.xa_index * PAGE_SIZE;
> + loff_t pos = (u64)xas.xa_index << PAGE_SHIFT;
> + unsigned int seek_size;
I've been preferring size_t for 'number of bytes in a page' because
I'm sure somebody is going to want a page larger than 2GB in the next
ten years.
next prev parent reply other threads:[~2021-04-22 1:18 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-22 0:35 [PATCH 0/2] mm/filemap: fix 5.12-rc regressions Hugh Dickins
2021-04-22 0:37 ` [PATCH 1/2] mm/filemap: fix find_lock_entries hang on 32-bit THP Hugh Dickins
2021-04-22 1:06 ` Matthew Wilcox
2021-04-22 0:39 ` [PATCH 2/2] mm/filemap: fix mapping_seek_hole_data on THP & 32-bit Hugh Dickins
2021-04-22 1:16 ` Matthew Wilcox [this message]
2021-04-22 5:55 ` Hugh Dickins
2021-04-22 20:46 ` Hugh Dickins
2021-04-22 20:48 ` [PATCH v2 " Hugh Dickins
2021-04-22 23:04 ` Andrew Morton
2021-04-23 17:22 ` Hugh Dickins
2021-04-23 19:29 ` Andrew Morton
2021-04-23 20:08 ` Hugh Dickins
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