On Wed, Jan 25, 2017 at 01:35:10PM -0500, Johannes Weiner wrote: > On Wed, Jan 25, 2017 at 08:55:22AM -0800, Srikar Dronamraju wrote: > > > > > > > > > For THPs page_check_address() always fails. It's better to split them > > > > > first before trying to replace. > > > > > > > > So what does this mean. uprobes simply fails to work when trying to > > > > place a probe into a THP memory region? > > > > > > Looks like we can end up with endless retry loop in uprobe_write_opcode(). > > > > > > > How come nobody noticed (and reported) this when using the feature? > > > > > > I guess it's not often used for anon memory. > > > > > > > The first time the breakpoint is hit on a page, it replaces the text > > page with anon page. Now lets assume we insert breakpoints in all the > > pages in a range. Here each page is individually replaced by a non THP > > anonpage. (since we dont have bulk breakpoint insertion support, > > breakpoint insertion happens one at a time). Now the only interesting > > case may be when each of these replaced pages happen to be physically > > contiguous so that THP kicks in to replace all of these pages with one > > THP page. Can happen in practice? > > > > Are there any other cases that I have missed? > > We use a hack in our applications where we open /proc/self/maps, copy > text segments to a staging area, then create overlay anon mappings on > top and copy the text back into them. Now we have THP-backed text and > very little iTLB pressure :-) Just use tmpfs with huge pages :) > That said, we haven't run into the uprobes issue yet. Is it possible to have uprobes in anon memory? -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
