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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <Y+PLrOM05FMCiTIg@infradead.org>
References: <Y+PLrOM05FMCiTIg@infradead.org> <Y+MydH2HZ7ihITli@infradead.org> <20230207171305.3716974-1-dhowells@redhat.com> <20230207171305.3716974-2-dhowells@redhat.com> <176199.1675872591@warthog.procyon.org.uk>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     dhowells@redhat.com, Jens Axboe <axboe@kernel.dk>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
        Jeff Layton <jlayton@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Hillf Danton <hdanton@sina.com>, linux-fsdevel@vger.kernel.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org,
        syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com,
        Christoph Hellwig <hch@lst.de>,
        John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH v12 01/10] vfs, iomap: Fix generic_file_splice_read() to avoid reversion of ITER_PIPE
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Date:   Thu, 09 Feb 2023 10:50:30 +0000
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Christoph Hellwig <hch@infradead.org> wrote:

> I defintively like the idea of killing ITER_PIPE.  Isn't the 16
> folios in a folio tree often much less than what we could fit into
> a single pipe buf?  Unless you have a file system that can use
> huge folios for buffered I/O and actually does this might significantly
> limit performance.

There's a loop there that repeats the filemap_get_pages() until either the
pipe is full or we hit EOF, the same as in filemap_read() (upon which this is
based).

I want to use filemap_get_pages() if I can as that does all the readahead
stuff.  What might be nice, though, is if I could tell it to return rather
than waiting for a folio to come uptodate if it has already returned a folio
so that I can push the other side of the splice along whilst the read is in
progress.

David