linux-kernel - Re: [PATCH v2 0/2] reclaim contended folios asynchronously instead of promoting them

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Date: Fri, 8 Mar 2024 04:56:46 +0000
From: Matthew Wilcox <willy@...radead.org>
To: lipeifeng@...o.com
Cc: 21cnbao@...il.com, akpm@...ux-foundation.org, david@...hat.com,
	osalvador@...e.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH v2 0/2] reclaim contended folios asynchronously instead
 of promoting them

On Fri, Mar 08, 2024 at 11:11:24AM +0800, lipeifeng@...o.com wrote:
> Commit 6d4675e60135 ("mm: don't be stuck to rmap lock on reclaim path")
> prevents the reclaim path from becoming stuck on the rmap lock. However,
> it reinserts those folios at the head of the LRU during shrink_folio_list,
> even if those folios are very cold.

This seems like a lot of new code.  Did you consider something simpler
like this?

Also, this is Minchan's patch you're complaining about.  Add him to the
cc.

+++ b/mm/vmscan.c
@@ -817,6 +817,7 @@ enum folio_references {
        FOLIOREF_RECLAIM,
        FOLIOREF_RECLAIM_CLEAN,
        FOLIOREF_KEEP,
+       FOLIOREF_RESCAN,
        FOLIOREF_ACTIVATE,
 };

@@ -837,9 +838,9 @@ static enum folio_references folio_check_references(struct folio *folio,
        if (vm_flags & VM_LOCKED)
                return FOLIOREF_ACTIVATE;

-       /* rmap lock contention: rotate */
+       /* rmap lock contention: keep at the tail */
        if (referenced_ptes == -1)
-               return FOLIOREF_KEEP;
+               return FOLIOREF_RESCAN;

        if (referenced_ptes) {
                /*
@@ -1164,6 +1165,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
                case FOLIOREF_ACTIVATE:
                        goto activate_locked;
                case FOLIOREF_KEEP:
+               case FOLIOREF_RESCAN:
                        stat->nr_ref_keep += nr_pages;
                        goto keep_locked;
                case FOLIOREF_RECLAIM:
@@ -1446,7 +1448,10 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 keep_locked:
                folio_unlock(folio);
 keep:
-               list_add(&folio->lru, &ret_folios);
+               if (references == FOLIOREF_RESCAN)
+                       list_add(&folio->lru, &rescan_folios);
+               else
+                       list_add(&folio->lru, &ret_folios);
                VM_BUG_ON_FOLIO(folio_test_lru(folio) ||
                                folio_test_unevictable(folio), folio);
        }