From: Matthew Wilcox <willy@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: hch@lst.de, trond.myklebust@primarydata.com,
Jens Axboe <axboe@kernel.dk>,
"Darrick J. Wong" <djwong@kernel.org>,
linux-block@vger.kernel.org, linux-xfs@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
darrick.wong@oracle.com, viro@zeniv.linux.org.uk,
jlayton@kernel.org, torvalds@linux-foundation.org,
linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 9/9] mm: Remove swap BIO paths and only use DIO paths
Date: Sat, 25 Sep 2021 18:09:46 +0100 [thread overview]
Message-ID: <YU9X2o74+aZP4iWV@casper.infradead.org> (raw)
In-Reply-To: <2396106.1632584202@warthog.procyon.org.uk>
On Sat, Sep 25, 2021 at 04:36:42PM +0100, David Howells wrote:
> Matthew Wilcox <willy@infradead.org> wrote:
>
> > On Fri, Sep 24, 2021 at 06:19:23PM +0100, David Howells wrote:
> > > Delete the BIO-generating swap read/write paths and always use ->swap_rw().
> > > This puts the mapping layer in the filesystem.
> >
> > Is SWP_FS_OPS now unused after this patch?
>
> Ummm. Interesting question - it's only used in swap_set_page_dirty():
>
> int swap_set_page_dirty(struct page *page)
> {
> struct swap_info_struct *sis = page_swap_info(page);
>
> if (data_race(sis->flags & SWP_FS_OPS)) {
> struct address_space *mapping = sis->swap_file->f_mapping;
>
> VM_BUG_ON_PAGE(!PageSwapCache(page), page);
> return mapping->a_ops->set_page_dirty(page);
> } else {
> return __set_page_dirty_no_writeback(page);
> }
> }
I suspect that's no longer necessary. NFS was the only filesystem
using SWP_FS_OPS and ...
fs/nfs/file.c: .set_page_dirty = __set_page_dirty_nobuffers,
so it's not like NFS does anything special to reserve memory to write
back swap pages.
> > Also, do we still need ->swap_activate and ->swap_deactivate?
>
> f2fs does quite a lot of work in its ->swap_activate(), as does btrfs. I'm
> not sure how necessary it is. cifs looks like it intends to use it, but it's
> not fully implemented yet. zonefs and nfs do some checking, including hole
> checking in nfs's case. nfs also does some setting up for the sunrpc
> transport.
>
> btrfs, cifs, f2fs and nfs all supply ->swap_deactivate() to undo the effects
> of the activation.
Right ... so my question really is, now that we're doing I/O through
aops->direct_IO (or ->swap_rw), do those magic things need to be done?
After all, open(O_DIRECT) doesn't do these same magic things. They're
really there to allow the direct-to-BIO path to work, and you're removing
that here.
next prev parent reply other threads:[~2021-09-25 17:11 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-24 17:17 [RFC][PATCH v3 0/9] mm: Use DIO for swap and fix NFS swapfiles David Howells
2021-09-24 17:18 ` [PATCH v3 1/9] mm: Remove the callback func argument from __swap_writepage() David Howells
2021-09-24 17:18 ` [PATCH v3 2/9] mm: Add 'supports' field to the address_space_operations to list features David Howells
2021-09-24 20:10 ` Matthew Wilcox
2021-09-24 17:18 ` [PATCH v3 3/9] mm: Make swap_readpage() void David Howells
2021-09-24 22:07 ` Matthew Wilcox
2021-09-24 17:18 ` [PATCH v3 4/9] Introduce IOCB_SWAP kiocb flag to trigger REQ_SWAP David Howells
2021-09-26 21:56 ` Dave Chinner
2021-09-24 17:18 ` [PATCH v3 5/9] mm: Make swap_readpage() for SWP_FS_OPS use ->swap_rw() not ->readpage() David Howells
2021-09-24 17:18 ` [PATCH v3 6/9] mm: Make __swap_writepage() do async DIO if asked for it David Howells
2021-09-24 17:19 ` [PATCH v3 7/9] nfs: Fix write to swapfile failure due to generic_write_checks() David Howells
2021-09-24 17:19 ` [PATCH v3 8/9] block, btrfs, ext4, xfs: Implement swap_rw David Howells
2021-09-24 17:19 ` [PATCH v3 9/9] mm: Remove swap BIO paths and only use DIO paths David Howells
2021-09-25 14:56 ` Matthew Wilcox
2021-09-25 15:36 ` David Howells
2021-09-25 17:09 ` Matthew Wilcox [this message]
2021-09-26 23:08 ` Damien Le Moal
2021-09-27 1:25 ` Dave Chinner
2021-09-27 1:41 ` Damien Le Moal
2021-09-27 20:03 ` David Sterba
2021-09-25 23:42 ` [RFC][PATCH v3 0/9] mm: Use DIO for swap and fix NFS swapfiles Dave Chinner
2021-09-26 3:10 ` Matthew Wilcox
2021-09-26 22:36 ` Dave Chinner
2021-09-27 20:07 ` David Sterba
2021-09-28 3:11 ` NeilBrown
2021-09-30 15:54 ` Steve French
2021-09-29 15:45 ` David Howells
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