On Wed, Feb 21, 2024 at 02:30:13PM -0800, Andrew Morton wrote: > On Sat, 17 Feb 2024 00:11:25 -0500 Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > > On Fri, Feb 16, 2024 at 2:24 AM Byungchul Park <byungchul@xxxxxx> wrote: > > > > > > On Fri, Feb 16, 2024 at 12:55:17AM -0500, Yu Zhao wrote: > > > > On Thu, Feb 8, 2024 at 1:18 AM Byungchul Park <byungchul@xxxxxx> wrote: > > > > > > > > > > With cache_trim_mode on, reclaim logic doesn't bother reclaiming anon > > > > > pages. However, it should be more careful to turn on the mode because > > > > > it's going to prevent anon pages from reclaimed even if there are huge > > > > > ammount of anon pages that are very cold so should be reclaimed. Even > > > > > worse, that can lead kswapd_failures to be MAX_RECLAIM_RETRIES and stop > > > > > until direct reclaim eventually works to resume kswapd. > > > > > > > > Is a theory or something observed in the real world? If it's the > > > > former, would this change risk breaking existing use cases? It's the > > > > > > I faced the latter case. > > > > > > > latter, where are the performance numbers to show what it looks like > > > > before and after this patch? > > > > Let me ask again: where are the performance numbers to show what it > > looks like before and after this patch? > > > > > Before: > > > > > > Whenever the system meets the condition to turn on cache_trim_mode but > > > few cache pages to trim, kswapd fails without scanning anon pages that > > > are plenty and cold for sure and it retries 8 times and looks *stopped > > > for ever*. > > Does "stopped for ever" mean that kswapd simply stops functioning? Yes. kswapd stops its functioning. Even worse, after being stopped, any request to wake up kswapd fails until ->kswapd_failures gets reset to 0 by direct reclaim or something. It's more like a bug fix than a performance improvement. > If so, that's a pretty serious issue. Please fully describe all of > this in the changelog. Please also address Yu Zhao's review comments > and send us a v2 patch? Thanks. I will post v2 with vmstat numbers between before and after. Byungchul
