On 5/23/24 3:08 PM, Matthew Wilcox wrote:
> On Mon, May 13, 2024 at 09:23:39PM +0800, Liu Wei wrote:
>> After commit (6be96d3ad3 fs: return if direct I/O will trigger writeback),
>
> If you're reporting problems with a particular commit, it's good form
> to cc the people who actually wrote that commit.
Yeah indeed...
>> when we issuing AIO with direct I/O and IOCB_NOWAIT on a block device, the
>> process context will not be blocked.
>>
>> However, if the device already has page cache in memory, EAGAIN will be
>> returned. And even when trying to reissue the AIO with direct I/O and
>> IOCB_NOWAIT again, we consistently receive EAGAIN.
-EAGAIN doesn't mean "just try again and it'll work".
>> Maybe a better way to deal with it: filemap_fdatawrite_range dirty pages
>> with WB_SYNC_NONE flag, and invalidate_mapping_pages unmapped pages at
>> the same time.
>>
>> Signed-off-by: Liu Wei <liuwei09@xxxxxxxx>
>> ---
>> mm/filemap.c | 9 ++++++++-
>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index 30de18c4fd28..1852a00caf31 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -2697,8 +2697,15 @@ int kiocb_invalidate_pages(struct kiocb *iocb, size_t count)
>>
>> if (iocb->ki_flags & IOCB_NOWAIT) {
>> /* we could block if there are any pages in the range */
>> - if (filemap_range_has_page(mapping, pos, end))
>> + if (filemap_range_has_page(mapping, pos, end)) {
>> + if (mapping_needs_writeback(mapping)) {
>> + __filemap_fdatawrite_range(mapping,
>> + pos, end, WB_SYNC_NONE);
>> + }
I don't think WB_SYNC_NONE tells it not to block, it just says not to
wait for it... So this won't work as-is.
>> + invalidate_mapping_pages(mapping,
>> + pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
>> return -EAGAIN;
>> + }
>> } else {
>> ret = filemap_write_and_wait_range(mapping, pos, end);
>> if (ret)
>> --
>> 2.42.1
>>
>>
>>
--
Jens Axboe
