Re: [LSF/MM/BPF TOPIC] tracing mapped pages for quicker boot performance

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 12 Jan 2023 20:35:53 +0000
Matthew Wilcox <willy@infradead.org> wrote:

> On Thu, Jan 12, 2023 at 01:21:53PM -0500, Steven Rostedt wrote:
> > What I would like to discuss, is if there could be a way to add some sort
> > of trace events that can tell an application exactly what pages in a file
> > are being read from disk, where there is no such races. Then an application
> > would simply have to read this information and store it, and then it can
> > use this information later to call readahead() on these locations of the
> > file so that they are available when needed.  
> 
> trace_mm_filemap_add_to_page_cache()?

Great! How do I translate this to files? Do I just do a full scan on the
entire device to find which file maps to an inode? And I'm guessing that
the ofs is the offset into the file?

(from a 5.10 modified kernel)

            <...>-177   [001]    13.166966: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776a0 pfn=2586272 ofs=1204224
            <...>-177   [001]    13.166968: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776a1 pfn=2586273 ofs=1208320
            <...>-177   [001]    13.166968: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776a2 pfn=2586274 ofs=1212416
            <...>-177   [001]    13.166969: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776a3 pfn=2586275 ofs=1216512
            <...>-177   [001]    13.166970: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776a4 pfn=2586276 ofs=1220608
            <...>-177   [001]    13.166971: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776a5 pfn=2586277 ofs=1224704
            <...>-177   [001]    13.166972: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776a6 pfn=2586278 ofs=1228800
            <...>-177   [001]    13.166972: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776a7 pfn=2586279 ofs=1232896
            <...>-177   [001]    13.166973: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776a8 pfn=2586280 ofs=1236992
            <...>-177   [001]    13.166974: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776a9 pfn=2586281 ofs=1241088
            <...>-177   [001]    13.166979: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776aa pfn=2586282 ofs=1245184
            <...>-177   [001]    13.166980: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776ab pfn=2586283 ofs=1249280
            <...>-177   [001]    13.166981: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776ac pfn=2586284 ofs=1253376
            <...>-177   [001]    13.166981: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776ad pfn=2586285 ofs=1257472
            <...>-177   [001]    13.166982: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776ae pfn=2586286 ofs=1261568
            <...>-177   [001]    13.166983: mm_filemap_add_to_page_cache: dev 259:5 ino 9b11 page=0x2776af pfn=2586287 ofs=1265664

The dev 259:5 is the root partition.

Doing the following:

 $ printf "%d\n" 0x9b11
39697

 $ sudo find / -xdev -inum 39697
/lib64/libc.so.6

I guess that's what I need to do. Thanks!

I'll try it out. But I'd still like to have an invite as I have lots of
other fun stuff to talk to you all about (mm, fs, and BPF) ;-)

-- Steve