The patch titled
mm: add comment why mark_page_accessed() would be better than pte_mkyoung() in follow_page()
has been added to the -mm tree. Its filename is
mm-add-comment-why-mark_page_accessed-would-be-better-than-pte_mkyoung-in-follow_page.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: mm: add comment why mark_page_accessed() would be better than pte_mkyoung() in follow_page()
From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
At first look, mark_page_accessed() in follow_page() seems a bit strange.
It seems pte_mkyoung() would be better consistent with other kernel code.
However, it is intentional. The commit log said:
------------------------------------------------
commit 9e45f61d69be9024a2e6bef3831fb04d90fac7a8
Author: akpm <akpm>
Date: Fri Aug 15 07:24:59 2003 +0000
[PATCH] Use mark_page_accessed() in follow_page()
Touching a page via follow_page() counts as a reference so we should be
either setting the referenced bit in the pte or running mark_page_accessed().
Altering the pte is tricky because we haven't implemented an atomic
pte_mkyoung(). And mark_page_accessed() is better anyway because it has more
aging state: it can move the page onto the active list.
BKrev: 3f3c8acbplT8FbwBVGtth7QmnqWkIw
------------------------------------------------
The atomic issue is still true nowadays. adding comment help to understand
code intention and it would be better.
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Hugh Dickins <hugh@xxxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 5 +++++
1 file changed, 5 insertions(+)
diff -puN mm/memory.c~mm-add-comment-why-mark_page_accessed-would-be-better-than-pte_mkyoung-in-follow_page mm/memory.c
--- a/mm/memory.c~mm-add-comment-why-mark_page_accessed-would-be-better-than-pte_mkyoung-in-follow_page
+++ a/mm/memory.c
@@ -1151,6 +1151,11 @@ struct page *follow_page(struct vm_area_
if ((flags & FOLL_WRITE) &&
!pte_dirty(pte) && !PageDirty(page))
set_page_dirty(page);
+ /*
+ * pte_mkyoung() would be more correct here, but atomic care
+ * is needed to avoid losing dirty bit: easier to
+ * mark_page_accessed().
+ */
mark_page_accessed(page);
}
unlock:
_
Patches currently in -mm which might be from kosaki.motohiro@xxxxxxxxxxxxxx are
vmalloc-add-__get_vm_area_caller.patch
vmalloc-add-__get_vm_area_caller-checkpatch-fixes.patch
linux-next.patch
mm-clean-up-for-early_pfn_to_nid.patch
mm-fix-memmap-init-for-handling-memory-hole.patch
get_mm_hiwater_xxx-trivial-s-define-inline.patch
swsusp-clean-up-shrink_all_zones.patch
swsusp-dont-fiddle-with-swappiness.patch
vmscan-rename-scmay_swap-to-may_unmap.patch
mm-introduce-for_each_populated_zone-macro.patch
mm-introduce-for_each_populated_zone-macro-cleanup.patch
mm-dont-call-mark_page_accessed-in-do_swap_page.patch
mm-update_page_reclaim_stat-is-called-from-page-fault-path.patch
mm-shrink_all_memory-use-scnr_reclaimed.patch
mm-shrink_all_memory-use-scnr_reclaimed-checkpatch-fixes.patch
vmscan-clip-swap_cluster_max-in-shrink_all_memory.patch
mm-add-comment-why-mark_page_accessed-would-be-better-than-pte_mkyoung-in-follow_page.patch
getrusage-fill-ru_maxrss-value.patch
softirq-introduce-statistics-for-softirq.patch
proc-export-statistics-for-softirq-to-proc.patch
proc-export-statistics-for-softirq-to-proc-fix.patch
proc-update-document-for-proc-softirqs-and-proc-stat.patch
memcg-remove-mem_cgroup_calc_mapped_ratio-take2.patch
memcg-remove-mem_cgroup_reclaim_imbalance-remnants.patch
ia64-implement-interrupt-enabling-rwlocks.patch
fs-symlink-write_begin-allocation-context-fix-reiser4-fix.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
