Re: [PATCH] tmpfs: Insert tmpfs cache pages to inactive list atfirst

[Hugh Dickins]

On Wed, 19 May 2010, KOSAKI Motohiro wrote:

> Shaohua Li reported parallel file copy on tmpfs can lead to
> OOM killer. This is regression of caused by commit 9ff473b9a7
> (vmscan: evict streaming IO first). Wow, It is 2 years old patch!
> 
> Currently, tmpfs file cache is inserted active list at first. It
> mean the insertion doesn't only increase numbers of pages in anon LRU,
> but also reduce anon scanning ratio. Therefore, vmscan will get totally
> confusion. It scan almost only file LRU even though the system have
> plenty unused tmpfs pages.
> 
> Historically, lru_cache_add_active_anon() was used by two reasons.
> 1) Intend to priotize shmem page rather than regular file cache.
> 2) Intend to avoid reclaim priority inversion of used once pages.
> 
> But we've lost both motivation because (1) Now we have separate
> anon and file LRU list. then, to insert active list doesn't help
> such priotize. (2) In past, one pte access bit will cause page
> activation. then to insert inactive list with pte access bit mean
> higher priority than to insert active list. Its priority inversion
> may lead to uninteded lru chun. but it was already solved by commit
> 645747462 (vmscan: detect mapped file pages used only once).
> (Thanks Hannes, you are great!)
> 
> Thus, now we can use lru_cache_add_anon() instead.
> 
> Reported-by: Shaohua Li <shaohua.li@xxxxxxxxx>
> Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>

Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>

Thanks - though I don't quite agree with your description: I can't
see why the lru_cache_add_active_anon() was ever justified - that
"active" came in along with the separate anon and file LRU lists.

Hugh
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