On May 25, 2021, at 3:26 PM, Matthew Wilcox <willy@xxxxxxxxxxxxx> 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. Sure, that's one solution for a 1TB laptop, but not large filesystems that may be hundreds of TB per device. I don't think the owners of Perlmutter (https://www.nersc.gov/systems/perlmutter/) could be convinced to avoid using 17PB of their flash to avoid the need for TRIM to work. :-) Cheers, Andreas
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