On Fri, Mar 04, 2022 at 09:09:01PM -0800, Hugh Dickins wrote: > It's not quite as simple as just removing the test (as Mikulas did): > xfstests generic/013 hung because splice from tmpfs failed on page not > up-to-date and page mapping unset. That can be fixed just by marking > the ZERO_PAGE as Uptodate, which of course it is; doing so here in > shmem_file_read_iter() is distasteful, but seems to be the best way. Shouldn't we set ZERO_PAGE uptodate during early init code as it, uh, is per definition uptodate all the time? > > My intention, though, was to stop using the ZERO_PAGE here altogether: > surely iov_iter_zero() is better for this case? Sadly not: it relies > on clear_user(), and the x86 clear_user() is slower than its copy_user(): > https://lore.kernel.org/lkml/2f5ca5e4-e250-a41c-11fb-a7f4ebc7e1c9@xxxxxxxxxx/ Oh, that's sad as just using clear_user would be the right thing to here. > But while we are still using the ZERO_PAGE, let's stop dirtying its > struct page cacheline with unnecessary get_page() and put_page(). > > Reported-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> > Reported-by: Lukas Czerner <lczerner@xxxxxxxxxx> > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> But except for maybe making sure that ZERO_PAGE is always marked uptodate this does looks good to me.
