From: "Huang, Ying" <ying.huang@intel.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Kairui Song <ryncsn@gmail.com>,
linux-mm@kvack.org, Kairui Song <kasong@tencent.com>,
Andrew Morton <akpm@linux-foundation.org>,
Chris Li <chrisl@kernel.org>,
Barry Song <v-songbaohua@oppo.com>,
Ryan Roberts <ryan.roberts@arm.com>, Neil Brown <neilb@suse.de>,
Minchan Kim <minchan@kernel.org>,
Hugh Dickins <hughd@google.com>,
David Hildenbrand <david@redhat.com>,
Yosry Ahmed <yosryahmed@google.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-nfs@vger.kernel.org,
Trond Myklebust <trond.myklebust@hammerspace.com>,
Anna Schumaker <anna@kernel.org>,
linux-afs@lists.infradead.org,
David Howells <dhowells@redhat.com>,
Marc Dionne <marc.dionne@auristor.com>
Subject: Re: [PATCH v2 7/8] mm: drop page_index/page_file_offset and convert swap helpers to use folio
Date: Wed, 24 Apr 2024 14:45:26 +0800 [thread overview]
Message-ID: <87jzkns1h5.fsf@yhuang6-desk2.ccr.corp.intel.com> (raw)
In-Reply-To: <ZiiFHTwgu8FGio1k@casper.infradead.org> (Matthew Wilcox's message of "Wed, 24 Apr 2024 05:05:49 +0100")
Hi, Matthew,
Matthew Wilcox <willy@infradead.org> writes:
> On Wed, Apr 24, 2024 at 10:17:04AM +0800, Huang, Ying wrote:
>> Kairui Song <ryncsn@gmail.com> writes:
>> > static inline loff_t folio_file_pos(struct folio *folio)
>> > {
>> > - return page_file_offset(&folio->page);
>> > + if (unlikely(folio_test_swapcache(folio)))
>> > + return __folio_swap_dev_pos(folio);
>> > + return ((loff_t)folio->index << PAGE_SHIFT);
>>
>> This still looks confusing for me. The function returns the byte
>> position of the folio in its file. But we returns the swap device
>> position of the folio.
>>
>> Tried to search folio_file_pos() usage. The 2 usage in page_io.c is
>> swap specific, we can use swap_dev_pos() directly.
>>
>> There are also other file system users (NFS and AFS) of
>> folio_file_pos(), I don't know why they need to work with swap
>> cache. Cced file system maintainers for help.
>
> Time for a history lesson!
>
> In d56b4ddf7781 (2012) we introduced page_file_index() and
> page_file_mapping() to support swap-over-NFS. Writes to the swapfile went
> through ->direct_IO but reads went through ->readpage. So NFS was changed
> to remove direct references to page->mapping and page->index because
> those aren't right for anon pages (or shmem pages being swapped out).
>
> In e1209d3a7a67 (2022), we stopped using ->readpage in favour of using
> ->swap_rw. Now we don't need to use page_file_*(); we get the swap_file
> and ki_pos directly in the swap_iocb. But there are still relics in NFS
> that nobody has dared rip out. And there are all the copy-and-pasted
> filesystems that use page_file_* because they don't know any better.
>
> We should delete page_file_*() and folio_file_*(). They shouldn't be
> needed any more.
Thanks a lot for your detailed explanation! Yes, this will simplify the
semantics and improve the readability of the corresponding code.
--
Best Regards,
Huang, Ying
next prev parent reply other threads:[~2024-04-24 6:47 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-23 17:03 [PATCH v2 0/8] mm/swap: optimize swap cache search space Kairui Song
2024-04-23 17:03 ` [PATCH v2 1/8] NFS: remove nfs_page_lengthg and usage of page_index Kairui Song
2024-04-23 17:03 ` [PATCH v2 2/8] nilfs2: drop " Kairui Song
2024-04-23 18:48 ` Ryusuke Konishi
2024-04-24 1:57 ` Kairui Song
2024-04-23 17:03 ` [PATCH v2 3/8] f2fs: " Kairui Song
2024-04-23 22:58 ` Matthew Wilcox
2024-04-28 3:17 ` Chao Yu
2024-04-23 17:03 ` [PATCH v2 4/8] ceph: " Kairui Song
2024-04-24 0:03 ` Xiubo Li
2024-04-23 17:03 ` [PATCH v2 5/8] cifs: drop usage of page_file_offset Kairui Song
2024-04-23 17:03 ` [PATCH v2 6/8] mm/swap: get the swap file offset directly Kairui Song
2024-04-23 17:03 ` [PATCH v2 7/8] mm: drop page_index/page_file_offset and convert swap helpers to use folio Kairui Song
2024-04-24 2:17 ` Huang, Ying
2024-04-24 2:56 ` Kairui Song
2024-04-24 4:05 ` Matthew Wilcox
2024-04-24 6:45 ` Huang, Ying [this message]
2024-04-24 8:48 ` Kairui Song
2024-04-23 17:03 ` [PATCH v2 8/8] mm/swap: reduce swap cache search space Kairui Song
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