perf: Do not waste PAGE_SIZE bytes for ALIGN(8) in perf_event_mmap_event() (3ea2f2b9) · Commits · 戴 / test

perf_event_mmap_event() does kzalloc(PATH_MAX + sizeof(u64)) to ensure we can align the size later. However this means that we actually allocate PAGE_SIZE * 2 buffer, seems too much. Change this code to allocate PATH_MAX==PAGE_SIZE bytes, but tell d_path() to not use the last sizeof(u64) bytes. Note: it is not clear why do we need __GFP_ZERO, see the next patch. Signed-off-by:

Oleg Nesterov <oleg@redhat.com> Signed-off-by:

Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20131016201004.GC23214@redhat.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/events/core.c

+8 −7

Original line number	Diff line number	Diff line
		@@ -5113,17 +5113,18 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
		if (file) {
		struct inode *inode;
		dev_t dev;
		/*
		* d_path works from the end of the rb backwards, so we
		* need to add enough zero bytes after the string to handle
		* the 64bit alignment we do later.
		*/
		buf = kzalloc(PATH_MAX + sizeof(u64), GFP_KERNEL);

		buf = kzalloc(PATH_MAX, GFP_KERNEL);
		if (!buf) {
		name = strncpy(tmp, "//enomem", sizeof(tmp));
		goto got_name;
		}
		name = d_path(&file->f_path, buf, PATH_MAX);
		/*
		* d_path() works from the end of the rb backwards, so we
		* need to add enough zero bytes after the string to handle
		* the 64bit alignment we do later.
		*/
		name = d_path(&file->f_path, buf, PATH_MAX - sizeof(u64));
		if (IS_ERR(name)) {
		name = strncpy(tmp, "//toolong", sizeof(tmp));
		goto got_name;

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