copy on write for splice() from file to pipe?
willy at infradead.org
Fri Feb 10 04:44:41 UTC 2023
On Fri, Feb 10, 2023 at 03:06:26PM +1100, Dave Chinner wrote:
> So while I was pondering the complexity of this and watching a great
> big shiny rocket create lots of heat, light and noise, it occurred
That was kind of fun
> to me that we already have a mechanism for preventing page cache
> data from being changed while the folios are under IO:
> SB_I_STABLE_WRITES and folio_wait_stable().
I thought about bringing that up, but it's not quite right. That works
great for writeback, but it only works for writeback. We'd need to track
another per-folio counter ... it'd be like the page pinning kerfuffle,
only worse. And for such a rare thing it seems like a poor use of 32
bits of per-page state. Not to mention that you can effectively block
all writes to a file for an indefinite time by splicing pages to a pipe
that you then never read from.
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