linux-kernel - Re: [PATCH 02/10] staging: erofs: fix race when the managed cache is enabled

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Date:   Thu, 22 Nov 2018 13:26:27 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Gao Xiang <gaoxiang25@...wei.com>
Cc:     devel@...verdev.osuosl.org, linux-erofs@...ts.ozlabs.org,
        Chao Yu <yuchao0@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>, weidu.du@...wei.com,
        Miao Xie <miaoxie@...wei.com>
Subject: Re: [PATCH 02/10] staging: erofs: fix race when the managed cache is
 enabled

On Thu, Nov 22, 2018 at 07:43:50PM +0800, Gao Xiang wrote:
> Hi Greg,
> 
> On 2018/11/22 19:06, Greg Kroah-Hartman wrote:
> > On Thu, Nov 22, 2018 at 06:42:52PM +0800, Gao Xiang wrote:
> >> Hi Greg,
> >>
> >> On 2018/11/22 18:17, Greg Kroah-Hartman wrote:
> >>> Any specific reason why you are not using the refcount.h api instead of
> >>> "doing it yourself" with atomic_inc/dec()?
> >>>
> >>> I'm not rejecting this, just curious.
> >> As I explained in the previous email,
> >> Re: [PATCH 04/10] staging: erofs: fix `erofs_workgroup_{try_to_freeze, unfreeze}'
> >>
> >> we need such a function when the value is >= 0, it plays as a refcount,
> >> but when the refcount == EROFS_LOCKED_MAGIC (<0, but not 0 as refcount.h),
> >> and actually there is no need to introduce a seperate spinlock_t because
> >> we don't actually care about its performance (rarely locked). and
> >> the corresponding struct is too large for now, we need to decrease its size.
> > Why do you need to decrease the size?  How many of these structures are
> > created?
> 
> As I said in the previous email, every compressed page will have a managed structure
> called erofs_workgroup, and it is heavily allocated like page/inode/dentry in the erofs.

Ugh, every page?  Ok, nevermind, I take back my objections.  You all are
crazy and need to do crazy things like this :)

greg k-h