Re: [f2fs-dev] [PATCH v2] f2fs: another way to set large folio by remembering inode number

On 05/26, Matthew Wilcox wrote:
> On Tue, May 26, 2026 at 01:21:33AM +0000, Jaegeuk Kim wrote:
> > On 05/24, Christoph Hellwig wrote:
> > > On Fri, May 22, 2026 at 02:04:59PM +0000, Jaegeuk Kim wrote:
> > > > This was a quick buddyinfo right after booting the device.
> > > > 
> > > > Before:
> > > > Node 0, zone   Normal  22684  42284  28704  16901   9515   4566   1854    673    181     36    758
> > > > 
> > > > After disabling EROFS large folio:
> > > > Node 0, zone   Normal   8486   4732   2175   1161    697    272     82     19      3      1    856
> > > 
> > > And what are you trying to say us with that?
> > 
> > This means, high-order pages were used up by EROFS which sets large folio by
> > default. So, I wanted to say the concern was based on actual data which was what
> > Mattew asked.
> 
> This isn't that though.  What you actually need is to show that high order
> allocations are _failing_.  The MM is far more complicated than you seem
> to understand.  There isn't a fixed number of large folios available;
> when we try to allocate memory, we do reclaim.  And if there's large
> folios on the LRU list, you'll get them.
> 
> If what you want is large folios readily available, then what you want
> is large folios used _everywhere_ because then they're easy to get!
> If there's small folios in use, you need to reclaim a lot of memory in
> order to reassemble large folios (it's the birthday paradox, similar to
> the hash collision problem).

Thanks for the feedback. Actually, I tried to do compact_memory before doing
read() for AI loading, but I got complaints where it took hundreds milliseconds
to run that compact_memory. Is there a good way to secure high-order pages before
that read()? It was quite hard to project when it will happen.

> 
> 
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