From: Matthew Wilcox <willy@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: Anna Schumaker <anna.schumaker@netapp.com>,
Trond Myklebust <trond.myklebust@hammerspace.com>,
Jeff Layton <jlayton@redhat.com>,
Steve French <sfrench@samba.org>,
Dominique Martinet <asmadeus@codewreck.org>,
Mike Marshall <hubcap@omnibond.com>,
Miklos Szeredi <miklos@szeredi.hu>,
Shyam Prasad N <nspmangalore@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-cachefs@redhat.com, linux-afs@lists.infradead.org,
linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org,
ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net,
devel@lists.orangefs.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Canvassing for network filesystem write size vs page size
Date: Fri, 6 Aug 2021 00:47:35 +0100 [thread overview]
Message-ID: <YQx4lx7vEbvmfBnE@casper.infradead.org> (raw)
In-Reply-To: <1219713.1628181333@warthog.procyon.org.uk>
On Thu, Aug 05, 2021 at 05:35:33PM +0100, David Howells wrote:
> With Willy's upcoming folio changes, from a filesystem point of view, we're
> going to be looking at folios instead of pages, where:
>
> - a folio is a contiguous collection of pages;
>
> - each page in the folio might be standard PAGE_SIZE page (4K or 64K, say) or
> a huge pages (say 2M each);
This is not a great way to explain folios.
If you're familiar with compound pages, a folio is a new type for
either a base page or the head page of a compound page; nothing more
and nothing less.
If you're not familiar with compound pages, a folio contains 2^n
contiguous pages. They are treated as a single unit.
> - a folio has one dirty flag and one writeback flag that applies to all
> constituent pages;
>
> - a complete folio currently is limited to PMD_SIZE or order 8, but could
> theoretically go up to about 2GiB before various integer fields have to be
> modified (not to mention the memory allocator).
Filesystems should not make an assumption about this ... I suspect
the optimum page size scales with I/O bandwidth; taking PCI bandwidth
as a reasonable proxy, it's doubled five times in twenty years.
> Willy is arguing that network filesystems should, except in certain very
> special situations (eg. O_SYNC), only write whole folios (limited to EOF).
I did also say that the write could be limited by, eg, a byte-range
lease on the file. If the client doesn't have permission to write
a byte range, then it doesn't need to write it back.
next prev parent reply other threads:[~2021-08-05 23:48 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <YQv+iwmhhZJ+/ndc@casper.infradead.org>
[not found] ` <YQvpDP/tdkG4MMGs@casper.infradead.org>
[not found] ` <YQvbiCubotHz6cN7@casper.infradead.org>
[not found] ` <1017390.1628158757@warthog.procyon.org.uk>
[not found] ` <1170464.1628168823@warthog.procyon.org.uk>
[not found] ` <1186271.1628174281@warthog.procyon.org.uk>
2021-08-05 16:35 ` Canvassing for network filesystem write size vs page size David Howells
2021-08-05 17:27 ` Linus Torvalds
2021-08-05 17:43 ` Trond Myklebust
2021-08-05 22:11 ` Matthew Wilcox
2021-08-06 13:42 ` David Howells
2021-08-06 14:17 ` Matthew Wilcox
2021-08-06 15:04 ` David Howells
2021-08-05 17:52 ` Adam Borowski
2021-08-05 18:50 ` Jeff Layton
2021-08-05 23:47 ` Matthew Wilcox [this message]
2021-08-06 13:44 ` David Howells
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