Re: [PATCH v4 0/1] mm: vmascan: retry folios written back while isolated for traditional LRU

[Andrew Morton <akpm@linux-foundation.org>]

On Mon,  9 Dec 2024 08:36:17 +0000 Chen Ridong <chenridong@huaweicloud.com> wrote:

> The commit 359a5e1416ca ("mm: multi-gen LRU: retry folios written back
> while isolated") only fixed the issue for mglru. However, this issue
> also exists in the traditional active/inactive LRU. Fix this issue
> in the same way for active/inactive lru.
> 
> What is fixed:
> The page reclaim isolates a batch of folios from the tail of one of the
> LRU lists and works on those folios one by one.  For a suitable
> swap-backed folio, if the swap device is async, it queues that folio for
> writeback.  After the page reclaim finishes an entire batch, it puts back
> the folios it queued for writeback to the head of the original LRU list.
> 
> In the meantime, the page writeback flushes the queued folios also by
> batches.  Its batching logic is independent from that of the page reclaim.
> For each of the folios it writes back, the page writeback calls
> folio_rotate_reclaimable() which tries to rotate a folio to the tail.
> 
> folio_rotate_reclaimable() only works for a folio after the page reclaim
> has put it back.  If an async swap device is fast enough, the page
> writeback can finish with that folio while the page reclaim is still
> working on the rest of the batch containing it.  In this case, that folio
> will remain at the head and the page reclaim will not retry it before
> reaching there.

For a single patch series I think it's best to just make it a single
patch!  No need for a [0/n]: just put all the info into the patch's
changelog.

The patch doesn't apply to current development kernels.  Please check
the mm-unstable branch of
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/, or
linux-next.

Please replace vmascan with vmscan in the title.