mm/khugepaged: map dirty/writeback pages failures to EAGAIN

Patch series "mm/khugepaged: fix dirty page handling for MADV_COLLAPSE",
v5.

MADV_COLLAPSE on file-backed mappings fails with -EINVAL when TEXT pages
are dirty. This affects scenarios like package/container updates or
executing binaries immediately after writing them, etc.

The issue is that collapse_file() triggers async writeback and returns
SCAN_FAIL (maps to -EINVAL), expecting khugepaged to revisit later. But
MADV_COLLAPSE is synchronous and userspace expects immediate success or
a clear retry signal.

Reproduction:
 - Compile or copy 2MB-aligned executable to XFS/ext4 FS
 - Call MADV_COLLAPSE on .text section
 - First call fails with -EINVAL (text pages dirty from copy)
 - Second call succeeds (async writeback completed)

Issue Report:
https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@amd.com

This patch (of 2):

When collapse_file encounters dirty or writeback pages in file-backed
mappings, it currently returns SCAN_FAIL which maps to -EINVAL.  This is
misleading as EINVAL suggests invalid arguments, whereas dirty/writeback
pages represent transient conditions that may resolve on retry.

Introduce SCAN_PAGE_DIRTY_OR_WRITEBACK to cover both dirty and writeback
states, mapping it to -EAGAIN.  For MADV_COLLAPSE, this provides userspace
with a clear signal that retry may succeed after writeback completes.  For
khugepaged, this is harmless as it will naturally revisit the range during
periodic scans after async writeback completes.

Link: https://lkml.kernel.org/r/20260118190939.8986-2-shivankg@amd.com
Link: https://lkml.kernel.org/r/20260118190939.8986-4-shivankg@amd.com
Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE")
Signed-off-by: Shivank Garg <shivankg@amd.com>
Reported-by: Branden Moore <Branden.Moore@amd.com>
Closes: https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@amd.com
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: wang lian <lianux.mm@gmail.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Barry Song <baohua@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index 4cde53b45a85941a0f0364fff2b4223b4603adbb..4e41bff318888a7c844806b67dafd3a6dfe4a922 100644 (file)
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/huge_memory.h
@@ -37,7 +37,8 @@
        EM( SCAN_PAGE_HAS_PRIVATE,      "page_has_private")             \
        EM( SCAN_STORE_FAILED,          "store_failed")                 \
        EM( SCAN_COPY_MC,               "copy_poisoned_page")           \
-       EMe(SCAN_PAGE_FILLED,           "page_filled")
+       EM( SCAN_PAGE_FILLED,           "page_filled")                  \
+       EMe(SCAN_PAGE_DIRTY_OR_WRITEBACK, "page_dirty_or_writeback")
 
 #undef EM
 #undef EMe

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 97d1b2824386fa735c17f5ce6173574653dcf3a1..219dfa2e523c852b4f4a9407fbe9f52b226866c9 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -58,6 +58,7 @@ enum scan_result {
        SCAN_STORE_FAILED,
        SCAN_COPY_MC,
        SCAN_PAGE_FILLED,
+       SCAN_PAGE_DIRTY_OR_WRITEBACK,
 };
 
 #define CREATE_TRACE_POINTS
@@ -1967,11 +1968,11 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
                                 */
                                xas_unlock_irq(&xas);
                                filemap_flush(mapping);
-                               result = SCAN_FAIL;
+                               result = SCAN_PAGE_DIRTY_OR_WRITEBACK;
                                goto xa_unlocked;
                        } else if (folio_test_writeback(folio)) {
                                xas_unlock_irq(&xas);
-                               result = SCAN_FAIL;
+                               result = SCAN_PAGE_DIRTY_OR_WRITEBACK;
                                goto xa_unlocked;
                        } else if (folio_trylock(folio)) {
                                folio_get(folio);
@@ -2018,7 +2019,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
                         * folio is dirty because it hasn't been flushed
                         * since first write.
                         */
-                       result = SCAN_FAIL;
+                       result = SCAN_PAGE_DIRTY_OR_WRITEBACK;
                        goto out_unlock;
                }
 
@@ -2747,6 +2748,7 @@ static int madvise_collapse_errno(enum scan_result r)
        case SCAN_PAGE_LRU:
        case SCAN_DEL_PAGE_LRU:
        case SCAN_PAGE_FILLED:
+       case SCAN_PAGE_DIRTY_OR_WRITEBACK:
                return -EAGAIN;
        /*
         * Other: Trying again likely not to succeed / error intrinsic to