From: Michal Hocko <mhocko@kernel.org>
To: Baoquan He <bhe@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, rppt@linux.ibm.com, osalvador@suse.de,
willy@infradead.org, william.kucharski@oracle.com
Subject: Re: [PATCH v2 2/4] mm/sparse: Optimize sparse_add_one_section()
Date: Tue, 26 Mar 2019 11:17:10 +0100 [thread overview]
Message-ID: <20190326101710.GN28406@dhcp22.suse.cz> (raw)
In-Reply-To: <20190326100817.GV3659@MiWiFi-R3L-srv>
On Tue 26-03-19 18:08:17, Baoquan He wrote:
> On 03/26/19 at 10:29am, Michal Hocko wrote:
> > On Tue 26-03-19 17:02:25, Baoquan He wrote:
> > > Reorder the allocation of usemap and memmap since usemap allocation
> > > is much simpler and easier. Otherwise hard work is done to make
> > > memmap ready, then have to rollback just because of usemap allocation
> > > failure.
> >
> > Is this really worth it? I can see that !VMEMMAP is doing memmap size
> > allocation which would be 2MB aka costly allocation but we do not do
> > __GFP_RETRY_MAYFAIL so the allocator backs off early.
>
> In !VMEMMAP case, it truly does simple allocation directly. surely
> usemap which size is 32 is smaller. So it doesn't matter that much who's
> ahead or who's behind. However, this benefit a little in VMEMMAP case.
How does it help there? The failure should be even much less probable
there because we simply fall back to a small 4kB pages and those
essentially never fail.
> And this make code a little cleaner, e.g the error handling at the end
> is taken away.
>
> >
> > > And also check if section is present earlier. Then don't bother to
> > > allocate usemap and memmap if yes.
> >
> > Moving the check up makes some sense.
> >
> > > Signed-off-by: Baoquan He <bhe@redhat.com>
> >
> > The patch is not incorrect but I am wondering whether it is really worth
> > it for the current code base. Is it fixing anything real or it is a mere
> > code shuffling to please an eye?
>
> It's not a fixing, just a tiny code refactorying inside
> sparse_add_one_section(), seems it doesn't worsen thing if I got the
> !VMEMMAP case correctly, not quite sure. I am fine to drop it if it's
> not worth. I could miss something in different cases.
Well, I usually prefer to not do micro-optimizations in a code that
really begs for a much larger surgery. There are other people working on
the code and patches like these might get into the way and cuase
conflicts without a very good justification.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-03-26 10:17 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-26 9:02 [PATCH v2 0/4] Clean up comments and codes in sparse_add_one_section() Baoquan He
2019-03-26 9:02 ` [PATCH v2 1/4] mm/sparse: Clean up the obsolete code comment Baoquan He
2019-03-26 9:23 ` Mike Rapoport
2019-03-26 9:23 ` Michal Hocko
2019-03-26 9:30 ` Baoquan He
2019-03-26 9:36 ` Chao Fan
2019-03-26 9:43 ` Baoquan He
2019-03-26 9:46 ` Chao Fan
2019-03-26 9:02 ` [PATCH v2 2/4] mm/sparse: Optimize sparse_add_one_section() Baoquan He
2019-03-26 9:23 ` Mike Rapoport
2019-03-26 9:29 ` Michal Hocko
2019-03-26 10:08 ` Baoquan He
2019-03-26 10:17 ` Michal Hocko [this message]
2019-03-26 13:45 ` Baoquan He
2019-03-26 13:57 ` Mike Rapoport
2019-03-26 14:03 ` Michal Hocko
2019-03-26 14:18 ` Baoquan He
2019-03-26 14:31 ` Michal Hocko
2019-03-26 22:57 ` Baoquan He
2019-03-26 9:02 ` [PATCH v2 3/4] mm/sparse: Rename function related to section memmap allocation/free Baoquan He
2019-03-26 9:02 ` [PATCH v2 4/4] drivers/base/memory.c: Rename the misleading parameter Baoquan He
2019-03-26 9:20 ` Rafael J. Wysocki
2019-03-26 9:33 ` Michal Hocko
2019-03-26 11:43 ` Matthew Wilcox
2019-03-26 12:42 ` Baoquan He
2019-03-29 6:44 ` [PATCH v2 0/4] Clean up comments and codes in sparse_add_one_section() Baoquan He
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