Date: Fri, 13 Oct 2017 16:31:50 +0000 (UTC) From: Alan Cox <alc@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r324601 - head/sys/kern Message-ID: <201710131631.v9DGVoLf089000@repo.freebsd.org>
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Author: alc Date: Fri Oct 13 16:31:50 2017 New Revision: 324601 URL: https://svnweb.freebsd.org/changeset/base/324601 Log: Address two problems with sendfile(..., SF_NOCACHE) and apply one "optimization". First, sendfile(..., SF_NOCACHE) frees pages without checking whether those pages are mapped. This can leave the system with mappings to free or repurposed pages. Second, a page can be busied between the time of the current busy test and acquiring the object lock. Essentially, the test performed before the object lock is acquired can only be regarded as an optimization to short-circuit further work on the page. It cannot, however, be relied upon to prove that it is safe to free the page. Third, when sendfile(..., SF_NOCACHE) was originally implemented, vm_page_deactivate_noreuse() did not yet exist. Use vm_page_deactivate_noreuse() instead of vm_page_deactivate(), because it comes closer to freeing the page. In collaboration with: glebius Discussed with: gallatin, kib, markj X-MFC after: r324448 Modified: head/sys/kern/kern_sendfile.c Modified: head/sys/kern/kern_sendfile.c ============================================================================== --- head/sys/kern/kern_sendfile.c Fri Oct 13 16:23:05 2017 (r324600) +++ head/sys/kern/kern_sendfile.c Fri Oct 13 16:31:50 2017 (r324601) @@ -143,10 +143,23 @@ sendfile_free_page(vm_page_t pg, bool nocache) vm_page_free(pg); else if (nocache) { if (!vm_page_xbusied(pg) && VM_OBJECT_TRYWLOCK(obj)) { - vm_page_free(pg); + bool freed; + + /* Only free unmapped pages. */ + if (obj->ref_count == 0 || + !pmap_page_is_mapped(pg)) + /* + * The busy test before the object is + * locked cannot be relied upon. + */ + freed = vm_page_try_to_free(pg); + else + freed = false; VM_OBJECT_WUNLOCK(obj); + if (!freed) + vm_page_deactivate_noreuse(pg); } else - vm_page_deactivate(pg); + vm_page_deactivate_noreuse(pg); } } vm_page_unlock(pg);
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