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Date: Tue, 25 May 2021 15:13:51 -0700 From: "Darrick J. Wong" <djwong@...nel.org> To: Matthew Wilcox <willy@...radead.org> Cc: Andreas Dilger <adilger@...ger.ca>, Josh Triplett <josh@...htriplett.org>, David Howells <dhowells@...hat.com>, Theodore Ts'o <tytso@....edu>, Chris Mason <clm@...com>, Ext4 Developers List <linux-ext4@...r.kernel.org>, xfs <linux-xfs@...r.kernel.org>, linux-btrfs <linux-btrfs@...r.kernel.org>, linux-cachefs@...hat.com, linux-fsdevel <linux-fsdevel@...r.kernel.org>, NeilBrown <neilb@...e.com> Subject: Re: How capacious and well-indexed are ext4, xfs and btrfs directories? On Tue, May 25, 2021 at 10:26:17PM +0100, Matthew Wilcox wrote: > On Tue, May 25, 2021 at 03:13:52PM -0600, Andreas Dilger wrote: > > Definitely "-o discard" is known to have a measurable performance impact, > > simply because it ends up sending a lot more requests to the block device, > > and those requests can be slow/block the queue, depending on underlying > > storage behavior. > > > > There was a patch pushed recently that targets "-o discard" performance: > > https://patchwork.ozlabs.org/project/linux-ext4/list/?series=244091 > > that needs a bit more work, but may be worthwhile to test if it improves > > your workload, and help put some weight behind landing it? > > This all seems very complicated. I have chosen with my current laptop > to "short stroke" the drive. That is, I discarded the entire bdev, > then partitioned it roughly in half. The second half has never seen > any writes. This effectively achieves the purpose of TRIM/discard; > there are a lot of unused LBAs, so the underlying flash translation layer > always has plenty of spare space when it needs to empty an erase block. > > Since the steady state of hard drives is full, I have to type 'make clean' > in my build trees more often than otherwise and remember to delete iso > images after i've had them lying around for a year, but I'd rather clean > up a little more often than get these weird performance glitches. > > And if I really do need half a terabyte of space temporarily, I can > always choose to use the fallow range for a while, then discard it again. I just let xfs_scrub run FITRIM on Sundays at 4:30am. ;) --D
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