linux-kernel - Re: [PATCH v20 0/7] Virtio-balloon Enhancement

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Message-Id: <201712192305.AAE21882.MtQHJOFFSFVOLO@I-love.SAKURA.ne.jp>
Date:   Tue, 19 Dec 2017 23:05:11 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     wei.w.wang@...el.com
Cc:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, mst@...hat.com,
        mhocko@...nel.org, akpm@...ux-foundation.org,
        mawilcox@...rosoft.com, david@...hat.com, cornelia.huck@...ibm.com,
        mgorman@...hsingularity.net, aarcange@...hat.com,
        amit.shah@...hat.com, pbonzini@...hat.com, willy@...radead.org,
        liliang.opensource@...il.com, yang.zhang.wz@...il.com,
        quan.xu0@...il.com, nilal@...hat.com, riel@...hat.com
Subject: Re: [PATCH v20 0/7] Virtio-balloon Enhancement

Wei Wang wrote:
> ChangeLog:
> v19->v20:
> 1) patch 1: xbitmap
> 	- add __rcu to "void **slot";
> 	- remove the exceptional path.
> 2) patch 3: xbitmap
> 	- DeveloperNotes: add an item to comment that the current bit range
> 	  related APIs operating on extremely large ranges (e.g.
>           [0, ULONG_MAX)) will take too long time. This can be optimized in
> 	  the future.
> 	- remove the exceptional path;
> 	- remove xb_preload_and_set();
> 	- reimplement xb_clear_bit_range to make its usage close to
> 	  bitmap_clear;
> 	- rename xb_find_next_set_bit to xb_find_set, and re-implement it
> 	  in a style close to find_next_bit;
> 	- rename xb_find_next_zero_bit to xb_find_clear, and re-implement
> 	  it in a stytle close to find_next_zero_bit;
> 	- separate the implementation of xb_find_set and xb_find_clear for
> 	  the convenience of future updates.

Removing exceptional path made this patch easier to read.
But what I meant is

  Can you eliminate exception path and fold all xbitmap patches into one, and
  post only one xbitmap patch without virtio-balloon changes? 

.

I still think we don't need xb_preload()/xb_preload_end().
I think xb_find_set() has a bug in !node path.

Also, please avoid unconditionally adding to builtin modules.
There are users who want to save even few KB.