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From:   Charan Teja Kalla <quic_charante@quicinc.com>
To:     <akpm@linux-foundation.org>, <surenb@google.com>,
        <hannes@cmpxchg.org>, <minchan@kernel.org>
CC:     <quic_pkondeti@quicinc.com>, <quic_smanapra@quicinc.com>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        Charan Teja Kalla <quic_charante@quicinc.com>
Subject: [PATCH V3] mm: madvise: fix uneven accounting of psi
Date:   Mon, 3 Jul 2023 19:36:41 +0530
Message-ID: <1688393201-11135-1-git-send-email-quic_charante@quicinc.com>
MIME-Version: 1.0
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Precedence: bulk

A folio turns into a Workingset during:
1) shrink_active_list() placing the folio from active to inactive list.
2) When a workingset transition is happening during the folio refault.

And when Workingset is set on a folio, PSI for memory can be accounted
during a) That folio is being reclaimed and b) Refault of that folio,
for usual reclaims.

This accounting of PSI for memory is not consistent for reclaim +
refault operation between usual reclaim and madvise(COLD/PAGEOUT) which
deactivate or proactively reclaim a folio:
a) A folio started at inactive and moved to active as part of accesses.
Workingset is absent on the folio thus refault of it when reclaimed
through MADV_PAGEOUT operation doesn't account for PSI.

b) When the same folio transition from inactive->active and then to
inactive through shrink_active_list(). Workingset is set on the folio
thus refault of it when reclaimed through MADV_PAGEOUT operation
accounts for PSI.

c) When the same folio is part of active list directly as a result of
folio refault and this was a workingset folio prior to eviction.
Workingset is set on the folio thus the refault of it when reclaimed
through MADV_PAGEOUT/MADV_COLD operation accounts for PSI.

d) MADV_COLD transfers the folio from active list to inactive
list. Such folios may not have the Workingset thus refault operation on
such folio doesn't account for PSI.

As said above, refault operation caused because of MADV_PAGEOUT on a
folio is accounts for memory PSI in b) and c) but not in a). Refault
caused by the reclaim of a folio on which MADV_COLD is performed
accounts memory PSI in c) but not in d). These behaviours are
inconsistent w.r.t usual reclaim + refault operation. Make this PSI
accounting always consistent by turning a folio into a workingset one
whenever it is leaving the active list. Also, accounting of PSI on a
folio whenever it leaves the active list as part of the
MADV_COLD/PAGEOUT operation helps the users whether they are operating
on proper folios[1].

[1] https://lore.kernel.org/all/20230605180013.GD221380@cmpxchg.org/

Suggested-by: Suren Baghdasaryan <surenb@google.com>
Reported-by: Sai Manobhiram Manapragada <quic_smanapra@quicinc.com>
Reported-by: Pavan Kondeti <quic_pkondeti@quicinc.com>
Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>
---
V3: Incorporated comments from Johannes/Pavan.

V2: Made changes as per the comments from Johannes/Suren.
    https://lore.kernel.org/all/1687861992-8722-1-git-send-email-quic_charante@quicinc.com/

V1: https://lore.kernel.org/all/1685531374-6091-1-git-send-email-quic_charante@quicinc.com/

 mm/madvise.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/madvise.c b/mm/madvise.c
index d9e7b42..d00a843 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -413,6 +413,8 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 
 		folio_clear_referenced(folio);
 		folio_test_clear_young(folio);
+		if (folio_test_active(folio))
+			folio_set_workingset(folio);
 		if (pageout) {
 			if (folio_isolate_lru(folio)) {
 				if (folio_test_unevictable(folio))
@@ -512,6 +514,8 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 		 */
 		folio_clear_referenced(folio);
 		folio_test_clear_young(folio);
+		if (folio_test_active(folio))
+			folio_set_workingset(folio);
 		if (pageout) {
 			if (folio_isolate_lru(folio)) {
 				if (folio_test_unevictable(folio))
-- 
2.7.4