在 2025/7/15 22:28, Jens Axboe 写道:
On 7/14/25 9:10 PM, Qi Han wrote:
Jens has already completed the development of uncached buffered I/O
in git [1], and in f2fs, the feature can be enabled simply by setting
the FOP_DONTCACHE flag in f2fs_file_operations.
You need to ensure that for any DONTCACHE IO that the completion is
routed via non-irq context, if applicable. I didn't verify that this is
the case for f2fs. Generally you can deduce this as well through
testing, I'd say the following cases would be interesting to test:
1) Normal DONTCACHE buffered read
2) Overwrite DONTCACHE buffered write
3) Append DONTCACHE buffered write
Test those with DEBUG_ATOMIC_SLEEP set in your config, and it that
doesn't complain, that's a great start.
For the above test cases as well, verify that page cache doesn't grow as
IO is performed. A bit is fine for things like meta data, but generally
you want to see it remain basically flat in terms of page cache usage.
Maybe this is all fine, like I said I didn't verify. Just mentioning it
for completeness sake.
Hi, Jens
Thanks for your suggestion. As I mentioned earlier in [1], in f2fs,
the regular buffered write path invokes folio_end_writeback from a
softirq context. Therefore, it seems that f2fs may not be suitable
for DONTCACHE I/O writes.
I’d like to ask a question: why is DONTCACHE I/O write restricted to
non-interrupt context only? Is it because dropping the page might be
too time-consuming to be done safely in interrupt context? This might
be a naive question, but I’d really appreciate your clarification.
Thanks in advance.
[1] https://lore.kernel.org/all/137c0a07-ea0a-48fa-acc4-3e0ec6368...@vivo.com/
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