On 3/23/22 12:48, Jaegeuk Kim wrote:
On 03/23, Christoph Hellwig wrote:
On Tue, Mar 22, 2022 at 10:22:50AM -0700, Linus Torvalds wrote:
On Mon, Mar 21, 2022 at 1:39 PM Jaegeuk Kim <[email protected]> wrote:
In this cycle, f2fs has some performance improvements for Android workloads such
as using read-unfair rwsems [...]
I've pulled this, but that read-unfair rwsem code looks incredibly
dodgy. Doing your own locking is always a bad sign, and it ahs
traditionally come back to bite us pretty much every time. At least it
uses real lock primitives, just in a really odd way.
FYI, Peter and I both pointed this out when the patches were posted
and NAKed the patch, but the feedback was ignored.
Christoph, I proposed,
"I've been waiting for a generic solution as suggested here. Until then, I'd
like
to keep this in f2fs *only* in order to ship the fix in products. Once there's
a right fix, let me drop or revise this patch again."
https://lore.kernel.org/linux-f2fs-devel/[email protected]/
I suspect f2fs may also need the 617f3ef95177 ("locking/rwsem: Remove
reader optimistic spinning") to give higher priority to writer. Please
let me know the test result when you are able to test v5.15 LTS to see
if these commits are able to address the f2fs issue.
I have some ideas of making a reader-unfair rwsem, but that requires
either the introduction of a set of new down_read() variants or keeping
the unfair state in the rwsem itself. I would like to make sure that
there is really a need for such a thing before working on it.
Cheers,
Longman
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