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[23.116.43.216]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7c7f55bca95sm47468617b3.39.2026.05.16.14.04.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 16 May 2026 14:04:11 -0700 (PDT) From: Ravi Jonnalagadda To: sj@kernel.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Cc: akpm@linux-foundation.org, corbet@lwn.net, bijan311@gmail.com, ajayjoshi@micron.com, honggyu.kim@sk.com, yunjeong.mun@sk.com, ravis.opensrc@gmail.com Subject: [RFC PATCH 5/5] mm/damon/paddr: add time budget to migration page walk Date: Sat, 16 May 2026 14:03:57 -0700 Message-ID: <20260516210357.2247-6-ravis.opensrc@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260516210357.2247-1-ravis.opensrc@gmail.com> References: <20260516210357.2247-1-ravis.opensrc@gmail.com> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On populated physical address ranges the pageblock skip optimization alone is insufficient — most pageblocks contain at least one allocated page, so the walk still iterates millions of PFNs. Add a 100ms wall-clock time budget to damon_pa_migrate(). Once the deadline is reached, the walk breaks out and migrates whatever folios have been collected so far. The time check is amortized by only calling ktime_get() every 4096 pages (~16MB of address space), adding negligible overhead to the fast path. Signed-off-by: Ravi Jonnalagadda --- mm/damon/paddr.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c index e844c990987b9..a2565287bc10f 100644 --- a/mm/damon/paddr.c +++ b/mm/damon/paddr.c @@ -14,6 +14,7 @@ #include #include #include +#include #include "../internal.h" #include "ops-common.h" @@ -254,6 +255,14 @@ static unsigned long damon_pa_deactivate_pages(struct damon_region *r, return damon_pa_de_activate(r, addr_unit, s, false, sz_filter_passed); } +/* Maximum wall-clock time to spend in a single migration walk (ns) */ +#define DAMON_PA_MIGRATE_BUDGET_NS (100 * NSEC_PER_MSEC) + +/* Check the time budget every 4096 pages (~16MB) to amortize ktime_get(). */ +#define DAMON_PA_MIGRATE_TIME_CHECK_PAGES 4096 +#define DAMON_PA_MIGRATE_TIME_CHECK_MASK \ + (DAMON_PA_MIGRATE_TIME_CHECK_PAGES - 1) + static unsigned long damon_pa_migrate(struct damon_region *r, unsigned long addr_unit, struct damos *s, unsigned long *sz_filter_passed) @@ -262,6 +271,7 @@ static unsigned long damon_pa_migrate(struct damon_region *r, LIST_HEAD(folio_list); struct folio *folio = NULL; unsigned long pfn; + ktime_t deadline = ktime_add_ns(ktime_get(), DAMON_PA_MIGRATE_BUDGET_NS); addr = damon_pa_phys_addr(r->ar.start, addr_unit); end = damon_pa_phys_addr(r->ar.end, addr_unit); @@ -283,6 +293,11 @@ static unsigned long damon_pa_migrate(struct damon_region *r, } } + /* Time budget: keep kdamond responsive on long migration walks. */ + if (!(pfn & DAMON_PA_MIGRATE_TIME_CHECK_MASK) && + ktime_after(ktime_get(), deadline)) + break; + folio = damon_get_folio(pfn); if (damon_pa_invalid_damos_folio(folio, s)) { addr += PAGE_SIZE; -- 2.43.0