On 06/02/2025 21:44, Darrick J. Wong wrote:
What is this checking? That something else already created a mapping in
the COW fork, so we want to bail out to get rid of it?
I want to check if some data is shared. In that case, we should unshare.
Why is it necessary to unshare? Userspace gave us a buffer of new
contents, and we're already prepared to write that out of place and
remap it.
fine, as long as the remap does what we need, then I won't bother with
this explicit unshare.
And I am not sure if that check is sufficient.
On the buffered write path, we may have something in a CoW fork - in that
case it should be flushed, right?
Flushed against what? Concurrent writeback or something? The directio
setup should have flushed dirty pagecache, so the only things left in
the COW fork are speculative preallocations. (IOWs, I don't understand
what needs to be flushed or why.)
ah, ok, as long as DIO would have flushed dirty relevant pagecache, then
we should be good.
Cheers,
John
