FAILED: patch "[PATCH] selftests/mm: compaction_test: support platform with huge" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x ab00ddd802f80e31fc9639c652d736fe3913feae
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025051246-book-chase-1d4c@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ab00ddd802f80e31fc9639c652d736fe3913feae Mon Sep 17 00:00:00 2001
From: Feng Tang <[email protected]>
Date: Wed, 23 Apr 2025 18:36:45 +0800
Subject: [PATCH] selftests/mm: compaction_test: support platform with huge
mount of memory

When running mm selftest to verify mm patches, 'compaction_test' case failed on an x86 server with 1TB memory. And the root cause is that it has too much free memory than what the test supports.

The test case tries to allocate 100000 huge pages, which is about 200 GB for that x86 server, and when it succeeds, it expects it's large than 1/3 of 80% of the free memory in system. This logic only works for platform with 750 GB ( 200 / (1/3) / 80% ) or less free memory, and may raise false alarm for others.

Fix it by changing the fixed page number to self-adjustable number according to the real number of free memory.

index 2c3a0eb6b22d..9bc4591c7b16 100644
@@ -90,6 +90,8 @@ int check_compaction(unsigned long mem_free, unsigned long hugepage_size,
 	int compaction_index = 0;
 	char nr_hugepages[20] = {0};
 	char init_nr_hugepages[24] = {0};
+	char target_nr_hugepages[24] = {0};
+	int slen;
 
 	snprintf(init_nr_hugepages, sizeof(init_nr_hugepages),
 		 "%lu", initial_nr_hugepages);

@@ -106,11 +108,18 @@ int check_compaction(unsigned long mem_free, unsigned long hugepage_size,
 		goto out;
 	}
 
-	/* Request a large number of huge pages. The Kernel will allocate
-	   as much as it can */
-	if (write(fd, "100000", (6*sizeof(char))) != (6*sizeof(char))) {
-		ksft_print_msg("Failed to write 100000 to /proc/sys/vm/nr_hugepages: %s\n",
-			       strerror(errno));
+	/*
+	 * Request huge pages for about half of the free memory. The Kernel
+	 * will allocate as much as it can, and we expect it will get at least 1/3
+	 */
+	nr_hugepages_ul = mem_free / hugepage_size / 2;
+	snprintf(target_nr_hugepages, sizeof(target_nr_hugepages),
+		 "%lu", nr_hugepages_ul);
+
+	slen = strlen(target_nr_hugepages);
+	if (write(fd, target_nr_hugepages, slen) != slen) {
+		ksft_print_msg("Failed to write %lu to /proc/sys/vm/nr_hugepages: %s\n",
+			       nr_hugepages_ul, strerror(errno));
 		goto close_fd;
 	}