AFAIK, The issue is not huge pages that applications opt in to and control; it's when they are "transparent", as in when the kernel "helpfully" decides when to use them. This can lead to significant pauses as the kernel decides that now is the time to rearrange your process's memory to be more or less huge-page-y. I have experienced this even with desktop java apps with relatively small heaps.
You can look for CONFIG_TRANSPARENT_HUGEPAGE in your kernel config. -Marshall On 08/07/2017 10:42 AM, Peter Veentjer wrote: > Hi Everyone, > > I have a failing understanding the problem with transparent huge pages. > > I 'understand' how normal pages work. A page is typically 4kb in a > virtual address space; each process has its own. > > I understand how the TLB fits in; a cache providing a mapping of virtual > to real addresses to speed up address conversion. > > I understand that using a large page e.g. 2mb instead of a 4kb page can > reduce pressure on the TLB. > > So till so far it looks like huge large pages makes a lot of sense; of > course at the expensive of wasting memory if only a small section of a > page is being used. > > The first part I don't understand is: why is it called transparent huge > pages? So what is transparent about it? > > The second part I'm failing to understand is: why can it cause problems? > There are quite a few applications that recommend disabling THP and I > recently helped a customer that was helped by disabling it. It seems > there is more going on behind the scene's than having an increased page > size. Is it caused due to fragmentation? So if a new page is needed and > memory is fragmented (due to smaller pages); that these pages need to be > compacted before a new page can be allocated? > > -- > You received this message because you are subscribed to the Google > Groups "mechanical-sympathy" group. > To unsubscribe from this group and stop receiving emails from it, send > an email to [email protected] > <mailto:[email protected]>. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "mechanical-sympathy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
