linux-kernel - Re: [PATCH v3 31/35] lib: add memory allocations report in show

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Date: Thu, 15 Feb 2024 18:54:25 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, Vlastimil Babka <vbabka@...e.cz>, 
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Subject: Re: [PATCH v3 31/35] lib: add memory allocations report in show_mem()

On Thu, Feb 15, 2024 at 03:19:33PM -0800, Dave Hansen wrote:
> On 2/15/24 15:07, Steven Rostedt wrote:
> > Just adding the patches increases the size by 5k. But the rest shows an
> > increase of 259k, and you are worried about 4k (and possibly less?)???
> 
> Doesn't the new page_ext thingy add a pointer per 'struct page', or
> ~0.2% of RAM, or ~32MB on a 16GB laptop?  I, too, am confused why 4k is
> even remotely an issue.

page_ext adds a separate per-page array; it itself does not add a
pointer to strugt page, it's an array lookup that uses the page pfn.

We do add a pointer to page_ext, and that's (for now) unavoidable
overhead - but we'll be looking at referencing code tags by index, and
if that works out we'll be able to kill the page_ext dependency and just
store the alloc tag index in page bits.