From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f178.google.com (mail-ob0-f178.google.com [209.85.214.178]) by kanga.kvack.org (Postfix) with ESMTP id C01E66B0070 for ; Wed, 25 Feb 2015 16:58:58 -0500 (EST) Received: by mail-ob0-f178.google.com with SMTP id uz6so6981402obc.9 for ; Wed, 25 Feb 2015 13:58:58 -0800 (PST) Received: from smtp2.provo.novell.com (smtp2.provo.novell.com. [137.65.250.81]) by mx.google.com with ESMTPS id r127si2954818oig.99.2015.02.25.13.58.55 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 25 Feb 2015 13:58:56 -0800 (PST) From: Davidlohr Bueso Subject: [PATCH 2/3] oprofile: reduce mmap_sem hold for mm->exe_file Date: Wed, 25 Feb 2015 13:58:36 -0800 Message-Id: <1424901517-25069-3-git-send-email-dave@stgolabs.net> In-Reply-To: <1424901517-25069-1-git-send-email-dave@stgolabs.net> References: <1424901517-25069-1-git-send-email-dave@stgolabs.net> Sender: owner-linux-mm@kvack.org List-ID: To: akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, dave@stgolabs.net, rric@kernel.org, oprofile-list@lists.sf.net, Davidlohr Bueso sync_buffer() needs the mmap_sem for two distinct operations, both only occurring upon user context switch handling: 1) Dealing with the exe_file. 2) Adding the dcookie data as we need to lookup the vma that backs it. This is done via add_sample() and add_data(). This patch isolates 1), for it will no longer need the mmap_sem for serialization. However, for now, make of the more standard get_mm_exe_file(), requiring only holding the mmap_sem to read the value, and relying on reference counting to make sure that the exe file won't dissappear underneath us while doing the get dcookie. As a consequence, for 2) we move the mmap_sem locking into where we really need it, in lookup_dcookie(). The benefits are twofold: reduce mmap_sem hold times, and cleaner code. Cc: Robert Richter Cc: oprofile-list@lists.sf.net Signed-off-by: Davidlohr Bueso --- drivers/oprofile/buffer_sync.c | 30 ++++++++++++++++-------------- 1 file changed, 16 insertions(+), 14 deletions(-) diff --git a/drivers/oprofile/buffer_sync.c b/drivers/oprofile/buffer_sync.c index d93b2b6..82f7000 100644 --- a/drivers/oprofile/buffer_sync.c +++ b/drivers/oprofile/buffer_sync.c @@ -21,6 +21,7 @@ * objects. */ +#include #include #include #include @@ -224,10 +225,18 @@ static inline unsigned long fast_get_dcookie(struct path *path) static unsigned long get_exec_dcookie(struct mm_struct *mm) { unsigned long cookie = NO_COOKIE; + struct file *exe_file; - if (mm && mm->exe_file) - cookie = fast_get_dcookie(&mm->exe_file->f_path); + if (!mm) + goto done; + + exe_file = get_mm_exe_file(mm); + if (!exe_file) + goto done; + cookie = fast_get_dcookie(&exe_file->f_path); + fput(exe_file); +done: return cookie; } @@ -236,6 +245,8 @@ static unsigned long get_exec_dcookie(struct mm_struct *mm) * pair that can then be added to the global event buffer. We make * sure to do this lookup before a mm->mmap modification happens so * we don't lose track. + * + * The caller must ensure the mm is not nil (ie: not a kernel thread). */ static unsigned long lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset) @@ -243,6 +254,7 @@ lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset) unsigned long cookie = NO_COOKIE; struct vm_area_struct *vma; + down_read(&mm->mmap_sem); for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) { if (addr < vma->vm_start || addr >= vma->vm_end) @@ -262,6 +274,7 @@ lookup_dcookie(struct mm_struct *mm, unsigned long addr, off_t *offset) if (!vma) cookie = INVALID_COOKIE; + up_read(&mm->mmap_sem); return cookie; } @@ -402,20 +415,9 @@ static void release_mm(struct mm_struct *mm) { if (!mm) return; - up_read(&mm->mmap_sem); mmput(mm); } - -static struct mm_struct *take_tasks_mm(struct task_struct *task) -{ - struct mm_struct *mm = get_task_mm(task); - if (mm) - down_read(&mm->mmap_sem); - return mm; -} - - static inline int is_code(unsigned long val) { return val == ESCAPE_CODE; @@ -532,7 +534,7 @@ void sync_buffer(int cpu) new = (struct task_struct *)val; oldmm = mm; release_mm(oldmm); - mm = take_tasks_mm(new); + mm = get_task_mm(new); if (mm != oldmm) cookie = get_exec_dcookie(mm); add_user_ctx_switch(new, cookie); -- 2.1.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org