From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B7F681C7662 for ; Tue, 3 Sep 2024 08:57:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725353860; cv=none; b=YIMjdH/YMf+2Ad+IusAJ7f6ahNZIfE6KFkI2waQRDxSKV69ng//1E5jKj93E35xUxWmfr4/M9ClTvuq+3PtEj2GLlsMkMVvaRJAfnSOP9NI678w5TY+sHxBj6HIrdRGGzq37wFbScf3tCiFNskcxtx3zcu77idiN5LK8VkOc6gs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725353860; c=relaxed/simple; bh=tVRH57/TZY4TyvdZgVZLBbfd3Au67M0mzxPujgYYjV4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qyTsDqVfciYfpP2VUbHnAC+9hn/+PT5VjsevWbO9WTv3YiUe2QvVNExBMnbC4CJgW7yNvFBD80w1NRhDUCqV39T3HR0Nconw7JD0X4CurrO/tV8abtrjGBI/yxBpAgfv7o51mGJI6o5KwXqCcsQIYBRaPW3pay8SeDDB6Cd8vSM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=VI/EIBrH; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="VI/EIBrH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9BF3EC4CEC4; Tue, 3 Sep 2024 08:57:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1725353860; bh=tVRH57/TZY4TyvdZgVZLBbfd3Au67M0mzxPujgYYjV4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VI/EIBrHrTzju1odFrLiNf7NVBrsC0aV4noXANAMZBNBJJejNxI/WAysFIvfUkVJT U9nGh7vFjX2X1XO96tAa8v7JV51FQcrk/3eHHoNg07iD/ilMVB5qddXFjunDcEcTNX vZnWYqYtQ2xLoV4b8zaNK+GDkdso6UzRglN8YJHg= Date: Tue, 3 Sep 2024 10:57:32 +0200 From: Greg Kroah-Hartman To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , Arve =?iso-8859-1?B?SGr4bm5lduVn?= , Todd Kjos , Martijn Coenen , Joel Fernandes , Christian Brauner , Carlos Llamas , Suren Baghdasaryan , Tangquan Zheng Subject: Re: [PATCH] binder_alloc: Move alloc_page() out of mmap_rwsem to reduce the lock duration Message-ID: <2024090325-sublet-unsworn-b6a3@gregkh> References: <20240902225009.34576-1-21cnbao@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240902225009.34576-1-21cnbao@gmail.com> On Tue, Sep 03, 2024 at 10:50:09AM +1200, Barry Song wrote: > From: Barry Song > > The mmap_write_lock() can block all access to the VMAs, for example page > faults. Performing memory allocation while holding this lock may trigger > direct reclamation, leading to others being queued in the rwsem for an > extended period. > We've observed that the allocation can sometimes take more than 300ms, > significantly blocking other threads. The user interface sometimes > becomes less responsive as a result. To prevent this, let's move the > allocation outside of the write lock. > A potential side effect could be an extra alloc_page() for the second > thread executing binder_install_single_page() while the first thread > has done it earlier. However, according to Tangquan's 48-hour profiling > using monkey, the likelihood of this occurring is minimal, with a ratio > of only 1 in 2400. Compared to the significantly costly rwsem, this is > negligible. > On the other hand, holding a write lock without making any VMA > modifications appears questionable and likely incorrect. While this > patch focuses on reducing the lock duration, future updates may aim > to eliminate the write lock entirely. > > Cc: Greg Kroah-Hartman > Cc: "Arve Hjønnevåg" > Cc: Todd Kjos > Cc: Martijn Coenen > Cc: Joel Fernandes > Cc: Christian Brauner > Cc: Carlos Llamas > Cc: Suren Baghdasaryan > Tested-by: Tangquan Zheng > Signed-off-by: Barry Song > --- > drivers/android/binder_alloc.c | 18 ++++++++++++++---- > 1 file changed, 14 insertions(+), 4 deletions(-) > > diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c > index b3acbc4174fb..f20074e23a7c 100644 > --- a/drivers/android/binder_alloc.c > +++ b/drivers/android/binder_alloc.c > @@ -227,13 +227,23 @@ static int binder_install_single_page(struct binder_alloc *alloc, > if (!mmget_not_zero(alloc->mm)) > return -ESRCH; > > + /* > + * Don't allocate page in mmap_write_lock, this can block > + * mmap_rwsem for a long time; Meanwhile, allocation failure > + * doesn't necessarily need to return -ENOMEM, if lru_page > + * has been installed, we can still return 0(success). > + */ > + page = alloc_page(GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO); But now you are allocating new pages even if binder_get_installed_page() is an error, right? Doesn't that slow things down? How was this benchmarked? > + > /* > * Protected with mmap_sem in write mode as multiple tasks > * might race to install the same page. > */ > mmap_write_lock(alloc->mm); > - if (binder_get_installed_page(lru_page)) > + if (binder_get_installed_page(lru_page)) { > + ret = 1; That is not a valid error value :( > goto out; > + } > > if (!alloc->vma) { > pr_err("%d: %s failed, no vma\n", alloc->pid, __func__); > @@ -241,7 +251,6 @@ static int binder_install_single_page(struct binder_alloc *alloc, > goto out; > } > > - page = alloc_page(GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO); > if (!page) { > pr_err("%d: failed to allocate page\n", alloc->pid); > ret = -ENOMEM; > @@ -252,7 +261,6 @@ static int binder_install_single_page(struct binder_alloc *alloc, > if (ret) { > pr_err("%d: %s failed to insert page at offset %lx with %d\n", > alloc->pid, __func__, addr - alloc->buffer, ret); > - __free_page(page); > ret = -ENOMEM; > goto out; > } > @@ -262,7 +270,9 @@ static int binder_install_single_page(struct binder_alloc *alloc, > out: > mmap_write_unlock(alloc->mm); > mmput_async(alloc->mm); > - return ret; > + if (ret && page) > + __free_page(page); > + return ret < 0 ? ret : 0; Please only use ? : for when you have to, otherwise please spell it out with a normal if statement: if (ret < 0) return ret; return 0; But, this is abusing the fact that you set "ret = 1" above, which is going to trip someone up in the future as that is NOT a normal coding pattern we have in the kernel, sorry. If you insist on this change, please rework it to not have that type of "positive means one thing, 0 means another, and negative means yet something else" please. thanks, greg k-h