在 2024/7/22 17:04, Michal Hocko 写道:
On Sat 20-07-24 07:41:19, Qu Wenruo wrote:
[...]
So according to the trend, I'm pretty sure VFS people will reject such
new interface just to skip accounting.
I would just give it a try with your usecase described. If this is a
nogo then the root cgroup workaround is still available.
I have submitted a patchset doing exactly that, and thankfully that's
the series where I got all the helpful feedbacks:
https://lore.kernel.org/linux-btrfs/92dea37a395781ee4d5cf8b16307801ccd8a5700.1720572937.git.wqu@xxxxxxxx/
Unfortunately I haven't get any feedback from the VFS guys.
Thus the GFP_NO_ACCOUNT solution looks more feasible.
So we have GFP_ACCOUNT to opt in for accounting and now we should be
adding GFP_NO_ACCOUNT to override it? This doesn't sound like a good use
of gfp flags (which we do not have infinitely) and it is also quite
confusing TBH.
The problem is, for filemap_add_folio(), we didn't specify GFP_ACCOUNT
(nor any other caller) but it is still doing the charge, due to the
mostly-correct assumption that all filemap page caches are accessible to
user space programs.
So one can argue that, cgroup is still charged even if no GFP_ACCOUNT is
specified.
But I get your point, indeed it's not that a good idea to introduce
GFP_NO_ACCOUNT.
Thanks,
Qu
