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From: Matthew Wilcox <willy@infradead.org>
To: "Weiny, Ira" <ira.weiny@intel.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [RFC 00/11] Remove 'order' argument from many mm functions
Date: Thu, 9 May 2019 11:29:02 -0700	[thread overview]
Message-ID: <20190509182902.GA11738@bombadil.infradead.org> (raw)
In-Reply-To: <2807E5FD2F6FDA4886F6618EAC48510E79D0CFDA@CRSMSX101.amr.corp.intel.com>

On Thu, May 09, 2019 at 04:48:39PM +0000, Weiny, Ira wrote:
> > On Wed, May 08, 2019 at 06:58:09PM -0700, Ira Weiny wrote:
> > > On Mon, May 06, 2019 at 09:05:58PM -0700, Matthew Wilcox wrote:
> > > > It's possible to save a few hundred bytes from the kernel text by
> > > > moving the 'order' argument into the GFP flags.  I had the idea
> > > > while I was playing with THP pagecache (notably, I didn't want to add an
> > 'order'
> > > > parameter to pagecache_get_page())
> > ...
> > > > Anyway, this is just a quick POC due to me being on an aeroplane for
> > > > most of today.  Maybe we don't want to spend five GFP bits on this.
> > > > Some bits of this could be pulled out and applied even if we don't
> > > > want to go for the main objective.  eg rmqueue_pcplist() doesn't use
> > > > its gfp_flags argument.
> > >
> > > Over all I may just be a simpleton WRT this but I'm not sure that the
> > > added complexity justifies the gain.
> > 
> > I'm disappointed that you see it as added complexity.  I see it as reducing
> > complexity.  With this patch, we can simply pass GFP_PMD as a flag to
> > pagecache_get_page(); without it, we have to add a fifth parameter to
> > pagecache_get_page() and change all the callers to pass '0'.
> 
> I don't disagree for pagecache_get_page().
> 
> I'm not saying we should not do this.  But this seems odd to me.
> 
> Again I'm probably just being a simpleton...

This concerns me, though.  I see it as being a simplification, but if
other people see it as a complication, then it's not.  Perhaps I didn't
take the patches far enough for you to see benefit?  We have quite the
thicket of .*alloc_page.* functions, and I can't keep them all straight.
Between taking, or not taking, the nodeid, the gfp mask, the order, a VMA
and random other crap; not to mention the NUMA vs !NUMA implementations,
this is crying out for simplification.

It doesn't help that I screwed up the __get_free_pages patch.  I should
have grepped and realised that we had over 200 callers and it's not
worth changing them all as part of this patchset.


  reply	other threads:[~2019-05-09 18:29 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-07  4:05 [RFC 00/11] Remove 'order' argument from many mm functions Matthew Wilcox
2019-05-07  4:05 ` [PATCH 01/11] fix function alignment Matthew Wilcox
2019-05-09 10:55   ` Kirill A. Shutemov
2019-05-07  4:06 ` [PATCH 02/11] mm: Pass order to __alloc_pages_nodemask in GFP flags Matthew Wilcox
2019-05-09  1:50   ` Ira Weiny
2019-05-09 13:58     ` Matthew Wilcox
2019-05-09 16:22       ` Weiny, Ira
2019-05-09 10:59   ` Kirill A. Shutemov
2019-05-07  4:06 ` [PATCH 03/11] mm: Pass order to __get_free_pages() " Matthew Wilcox
2019-05-07  4:06 ` [PATCH 04/11] mm: Pass order to prep_new_page " Matthew Wilcox
2019-05-07  4:06 ` [PATCH 05/11] mm: Remove gfp_flags argument from rmqueue_pcplist Matthew Wilcox
2019-05-07  4:06 ` [PATCH 06/11] mm: Pass order to rmqueue in GFP flags Matthew Wilcox
2019-05-07  4:06 ` [PATCH 07/11] mm: Pass order to get_page_from_freelist " Matthew Wilcox
2019-05-07  4:06 ` [PATCH 08/11] mm: Pass order to __alloc_pages_cpuset_fallback " Matthew Wilcox
2019-05-07  4:06 ` [PATCH 09/11] mm: Pass order to prepare_alloc_pages " Matthew Wilcox
2019-05-07  4:06 ` [PATCH 10/11] mm: Pass order to try_to_free_pages " Matthew Wilcox
2019-05-07  4:06 ` [PATCH 11/11] mm: Pass order to node_reclaim() " Matthew Wilcox
2019-05-09  1:58 ` [RFC 00/11] Remove 'order' argument from many mm functions Ira Weiny
2019-05-09 14:07   ` Matthew Wilcox
2019-05-09 16:48     ` Weiny, Ira
2019-05-09 18:29       ` Matthew Wilcox [this message]
2019-05-29 21:44         ` Ira Weiny
2019-05-09 11:07 ` Kirill A. Shutemov
2019-05-14 14:51   ` Matthew Wilcox

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